Foundations · 30 minutes
Cryptocurrency 101
What a coin actually is, how a blockchain stops people cheating, who really holds your money, and where the risks and rules sit in 2026. No trading tips, no hype — just the mechanics.
Each new block carries a fingerprint of the one before it. Change any old block and every fingerprint after it breaks.
Teal = proved by the network
Facts anyone can verify independently with maths: who signed a transaction, what the ledger says, how many coins exist.
Amber = you are trusting someone
Claims that rest on a company, a founder or a promise: an exchange's balance page, a stablecoin's reserves, a project's roadmap.
Those two colours run through every module and lab in this course. Almost every crypto mistake comes from reading an amber thing as if it were teal.
What a cryptocurrency actually is
3 min read
Start by deleting the mental image of a coin. There is no file on your computer called bitcoin.dat that you can copy, and nothing physical changes hands. A cryptocurrency is a shared ledger — a list of transactions that thousands of independent computers each keep a full copy of, and that all of them agree on.
"Owning 0.4 BTC" means the ledger contains entries adding up to 0.4 BTC that only your secret key can spend. That is the whole thing. The coin is the entry; the network is the accountant.
Compare that to the money in your bank account, which is also just an entry in a ledger. The difference is who is allowed to edit it:
| Question | Bank money | Cryptocurrency |
|---|---|---|
| Who updates the ledger? | One institution | A network following shared rules |
| Who can freeze or reverse it? | The bank, a court, a regulator | Nobody, once confirmed |
| Who covers you if it goes wrong? | Deposit insurance, chargebacks | Usually nobody |
| Who decides how much exists? | Central bank policy | Software rules set in advance |
Notice the trade is symmetrical, not one-sided. You gain censorship-resistance and a supply schedule nobody can quietly change. You give up the safety net. Both columns of that table are honest descriptions of a real system with real users; a course that only shows you one column is selling something.
Bitcoin, launched in January 2009 by the pseudonymous Satoshi Nakamoto, was the first working version of this idea. Everything since — Ethereum, Solana, stablecoins, tokens, NFTs — is a variation on the same core move: replace the trusted middle-man with a ledger that strangers can verify for themselves.
Three questions that cut through any crypto pitch
1. What does this ledger let me verify myself, and what am I taking on trust? 2. If this project's team disappeared tomorrow, does the thing still work? 3. Where does the money for my return come from — a real revenue source, or the next buyer?
3Blue1Brown, "But how does bitcoin actually work?" (~26 min) — the clearest visual derivation of the whole system from first principles. Open on YouTube
Hashes, blocks and why tampering fails
4 min read
A hash function takes any input — a word, a contract, a 4GB video — and produces a fixed-length fingerprint, usually written as 64 hexadecimal characters. Three properties make it useful:
- Deterministic: the same input always gives the same fingerprint.
- Avalanche effect: change one character of the input and the entire fingerprint changes, unpredictably.
- One-way: given a fingerprint, there is no shortcut back to the input. You can only guess and check.
Try it. Type anything below and watch what happens when you add a full stop.
The fingerprint machine
Real SHA-256, computed in your browser. Nothing is sent anywhere.
From fingerprint to chain
A block is a bundle of transactions plus one extra ingredient: the hash of the previous block. That single detail is what makes the structure a chain. Block 4 contains a fingerprint of block 3, which contains a fingerprint of block 2, and so on back to the first block ever made.
Now imagine you want to erase a payment you made three blocks ago. You edit the block. Its fingerprint changes instantly (avalanche effect). But block 4 still stores the old fingerprint, so the link is visibly broken — and so is every link after it. To hide the edit you would have to rebuild every subsequent block, faster than the rest of the world is building new ones.
Break the chain
Four linked blocks. Edit the data in any block and watch the damage spread to the right. "Valid" here means the block's hash starts with 0000 — a toy version of the difficulty rule real networks use.
The honest version of "immutable"
Blockchains are not magically unchangeable. They are expensive to change. Rewriting history means out-computing or out-staking the rest of the network, which costs more than the fraud is usually worth. That is an economic guarantee, not a physical law — and on small, low-activity networks it has been broken in practice.
Anders Brownworth, "Blockchain 101 — A Visual Demo" (~17 min) — the same tamper demo you just used, built up step by step. Open on YouTube
Keys, wallets and who actually holds your money
4 min read
Every crypto account starts with a private key: a very large random number. Run it through some one-way maths and you get a public key, and from that, an address — the string you give people so they can pay you. The arrow only runs one way. An address reveals nothing about the key that controls it.
private key → public key → address
easy easy (reversing either step: computationally hopeless)
To spend, you use the private key to produce a digital signature over the transaction. Anyone can check the signature against your public key, and the check proves two things at once: the transaction came from the key's owner, and not a character of it has been altered since. This is pure teal — no company vouches for you, the maths does.
A wallet stores keys. It does not store coins; the coins never leave the ledger. Most wallets today derive all your keys from a single seed phrase of 12 or 24 ordinary English words. Those words are the money. Anyone who reads them can empty the wallet from anywhere on earth, instantly and irreversibly.
The custody question
| Approach | Who holds the keys | Real risk |
|---|---|---|
| Exchange account (custodial) | The company | Company failure, freeze, hack, or your account being locked. Your balance page is an IOU, not the ledger. |
| Software wallet (hot) | You, on an internet-connected device | Malware, phishing sites, malicious token approvals |
| Hardware wallet (cold) | You, on an offline device | Losing the device and the seed phrase; buying a tampered device |
"Not your keys, not your coins" is the slogan, and it is broadly right — but self-custody moves the risk rather than removing it. Exchanges have lost customer funds; individuals have lost far more to forgotten seed phrases, house fires and clipboard malware. The correct answer depends on how much you hold and how competent you are at operational security, which is exactly what the next lab is for.
Custody chooser
Answer three questions. This is a rough heuristic for thinking through the trade-off, not personal advice.
Small — pocket money
Anders Brownworth, part two — public/private key pairs, signatures and how an address is derived. Open on YouTube
Mining, staking and the cost of agreement
4 min read
Thousands of computers hold the ledger, so something has to decide whose version of the next block wins. That mechanism is called consensus, and there are two dominant designs.
Proof of work (Bitcoin)
Miners race to find a number — the nonce — that makes their block's hash start with a long run of zeros, exactly like Lab 2 but vastly harder. There is no clever method; it is trillions of guesses per second. The winner earns newly created coins plus transaction fees, and the network auto-adjusts difficulty so a block appears roughly every ten minutes.
The energy cost is the point: rewriting history means redoing all that work while the honest network keeps building. It is also the main criticism, and a fair one. Bitcoin's issuance is cut in half roughly every four years — the halving — heading to a hard ceiling of 21 million coins. About 20.07 million had been issued by August 2026, so more than 95% of all bitcoin that will ever exist already does.
Proof of stake (Ethereum and most newer chains)
Instead of burning electricity, validators lock up coins as collateral. The protocol picks who proposes each block, and a validator caught cheating has their stake destroyed — slashing. Ethereum switched to this model in September 2022 and cut its energy use by over 99%. The trade-off critics point to: influence is proportional to wealth, and large staking providers concentrate a meaningful share of validators.
| Proof of work | Proof of stake | |
|---|---|---|
| Cost to attack | Buy over half the world's hashpower and its electricity | Buy a controlling share of staked coins and accept losing it |
| Energy | High by design | Negligible |
| Reward to participants | Block subsidy + fees | Staking yield from issuance + fees |
| Common concern | Environmental cost, mining concentration | Wealth concentration, provider centralisation |
Two practical consequences for you as a user. First, confirmations: a transaction is not final the second you send it, it gets steadily harder to reverse as blocks pile on top. Second, fees: you are bidding for limited block space, so costs spike when the network is busy and have nothing to do with how much you are sending.
"Staking rewards" are not interest
Protocol staking pays you newly issued coins for helping secure a network — denominated in a volatile asset, with your capital sometimes locked. A platform advertising a fixed double-digit dollar yield on your crypto is doing something else entirely: lending it out, or paying old depositors with new ones. That distinction has bankrupted several large firms and a lot of their customers.
The crypto zoo: coins, tokens and stablecoins
4 min read
Trackers list well over seventeen thousand crypto assets. Almost all of them fall into five buckets, and knowing which bucket you are looking at tells you most of what matters.
| Bucket | Examples | What it is for | Where the risk sits |
|---|---|---|---|
| Base-layer money | Bitcoin | Scarce, hard-to-censor digital bearer asset | Price volatility; nothing generates cash flow |
| Smart-contract platforms | Ethereum, Solana | Programmable ledgers that run application code | Bugs in contracts, network outages, competition |
| Stablecoins | USDT, USDC | Dollar-pegged tokens for payments and parking cash | Reserve quality and issuer solvency — pure amber |
| Application tokens & NFTs | Exchange tokens, in-game items | Access, governance votes, provable ownership records | Whether anyone actually needs the thing |
| Memecoins | Dog- and celebrity-themed coins | Speculation and community, explicitly | Total loss is normal; supply often controlled by insiders |
Stablecoins deserve their own paragraph
They are roughly $300 billion of the market and are the plumbing most crypto activity actually runs on — over 90% of Brazilian crypto flows, for instance, are stablecoin-related. A dollar stablecoin is a promise that the issuer holds a real dollar (or a Treasury bill) for every token. That promise is a company's, not the network's. The token moving on-chain is teal; the dollar behind it is amber, and the entire value depends on the amber part being true.
The US now has a federal framework for this. The GENIUS Act, signed on 18 July 2025, sets who may issue payment stablecoins, requires 1:1 reserves, and bans issuers from paying interest to holders. Algorithmic stablecoins that tried to hold a peg with trading incentives rather than reserves have collapsed before, wiping out tens of billions of dollars in 2022.
Two numbers that mislead beginners
Market cap is price multiplied by circulating supply — it is not money that has been "invested" and not money you could get out. A thin market can post a billion-dollar cap on a few million dollars of real buying. Fully diluted valuation counts tokens that do not exist yet; if 80% of supply unlocks to insiders next year, today's price is competing with tomorrow's sellers.
A short explainer on stablecoins and the new rules around them. Open on YouTube
Buying it: fees, spreads and volatility
4 min read
Most people buy on a centralised exchange: verify identity, deposit currency, place an order. Four separate costs hide in that flow, and beginners usually only notice the first one.
- Trading fee — a percentage of the order, often lower on "advanced" screens than the simple buy button.
- Spread — the gap between buy and sell price. Instant-buy widgets frequently bake in a wide one, so the quoted "zero fee" is not free.
- Network fee — paid to the blockchain when you withdraw to your own wallet. Depends on network congestion, not on your amount.
- Spread on the way out — you pay again when you sell. Round-trip cost is what actually matters.
Then there is volatility, which dwarfs all of it. Bitcoin traded around $64,200 on 12 August 2026 — roughly 49% below its record high of $126,080 set on 6 October 2025, and down about 27% since January 2026. That is not an unusual episode. It is the normal texture of the asset class, and the same pattern has repeated through every cycle since 2011.
Drawdown maths is brutally asymmetric
A 50% fall needs a 100% rise to get back to even. A 75% fall needs a 300% rise. This is why position sizing matters far more than entry timing: the question is not "will it recover" but "can I survive the wait without selling".
Volatility and cost sandbox
Uses a fictional 24-month price path for an invented asset called TEST. It is not a forecast, not historical data, and not any real coin — the point is to feel how fees and drawdowns behave, not to predict anything.
One more access route worth knowing: since 2024, US spot Bitcoin and Ethereum exchange-traded funds let people hold exposure inside an ordinary brokerage account. You get familiar tax paperwork and custody handled for you, and you give up ever holding the keys — a deliberately amber choice, made explicit.
Scams, security and the mistakes beginners actually make
4 min read
This is the module that saves people money. In its 2025 Internet Crime Report, published April 2026, the FBI's IC3 logged 181,565 cryptocurrency-related complaints totalling more than $11 billion in losses — up 22% year on year, and more than half of all reported cybercrime losses. Investment fraud was the single largest category, and roughly 72% of those incidents involved crypto.
The patterns that repeat
- Pig butchering. Weeks or months of friendly contact from a wrong-number text, dating app or LinkedIn message, then an introduction to a professional-looking platform. Small withdrawals work. Large ones require a "tax" or "unlock fee". The platform is fabricated.
- Recovery scams. Fake law firms and fake officials targeting people who already lost money — 10,500 complaints and $1.4 billion in 2025 alone. Some impersonated IC3 staff.
- Seed phrase phishing. Fake wallet support, fake "validation" pages, fake airdrops. No legitimate service will ever need your 12 or 24 words. Ever.
- Malicious approvals. Connecting a wallet to a scam site and signing a transaction that grants unlimited spending permission over your tokens.
- AI-assisted everything. 2025 was the first year IC3 tracked AI as a descriptor: 22,000+ complaints, $893 million in losses. Bad grammar and clumsy fakes are no longer reliable tells.
Spot the red flag
Five fictional scenarios. Decide whether each is a normal situation or a scam pattern, then check.
A security baseline that covers most of it
- Write your seed phrase on paper or metal. Never photograph it, never type it into anything, never store it in cloud notes.
- Use an authenticator app rather than SMS for exchange two-factor — SIM-swap attacks are routine.
- Bookmark exchange and wallet URLs. Search-ad phishing is one of the most reliable attack routes there is.
- Send a small test transaction first, always. Crypto transfers cannot be recalled.
- Treat any guaranteed return, any urgency, and any "you must pay a fee to withdraw" as disqualifying on the spot.
- Keep large holdings on a hardware wallet and small spending amounts hot, the way you would a safe and a purse.
If someone contacted you first, the base rate is bad
Unsolicited investment help through a dating app, social DM, WhatsApp group or "wrong number" text is the single most common opening move in the FBI's data. Losses cluster among educated adults in their mid-30s to early 50s, often during a hard patch — divorce, bereavement, job loss. Nobody is too smart for this; the con is engineered around loneliness and trust, not stupidity.
Tax, rules and disclosure in 2026
3 min read
Rules vary enormously by country and change fast. What follows is a snapshot of the US position as of August 2026, offered so you know which questions to ask a professional — not as tax or legal advice.
Tax: crypto is property, not currency
Under IRS Notice 2014-21, US taxpayers treat crypto as property. The practical consequence surprises people: selling for dollars, swapping one coin for another, and paying for goods are all potentially taxable disposals. Buying and simply holding is not.
- Form 1099-DA arrived for the first time in early 2026, covering 2025 sales. That first round reports gross proceeds only — not what you paid — so many taxpayers had to supply their own cost basis.
- Cost-basis reporting is phased in for 2026 transactions, appearing on forms in early 2027.
- The "universal" method of pooling one asset across all your wallets has been eliminated; basis is tracked per wallet or account. Keep records accordingly.
- Transfers between your own wallets are not sales, but an exchange receiving coins from outside may report a zero basis, which looks like 100% gain until you correct it.
Regulation: two halves of a framework
The GENIUS Act (signed 18 July 2025) covers payment stablecoins — issuance, reserves, disclosure. The CLARITY Act would cover everything else: which tokens count as securities versus digital commodities, and whether the SEC or CFTC supervises a given market. It passed the House 294–134 in July 2025 and cleared the Senate Banking Committee 15–9 on 14 May 2026, but as of August 2026 it has stalled in the full Senate.
In the meantime, agencies are filling the gap: a joint SEC–CFTC classification published 17 March 2026 treated sixteen major tokens as digital commodities. Guidance like that can be reversed by a future administration in a way that a statute cannot. In the EU, the MiCA regime has been the unified rulebook since 2024, and rules elsewhere differ again — location matters.
If you publish about crypto, disclosure is not optional
Promoting a token you hold, or one you were paid to mention, without saying so has produced enforcement actions and settlements against celebrities and creators in several jurisdictions. State your holdings, label paid promotion clearly, and keep "not financial advice" as an honest description of what you are doing rather than a legal shield — it isn't one.
Where to go next
If you want to keep going: read the original Bitcoin white paper (nine pages, more readable than you expect), then set up a wallet on a test network where the coins are worthless and practise sending, receiving and restoring from a seed phrase. Making every beginner mistake with fake money is the cheapest tuition available.
Ten questions
Answer all ten, then score. Explanations appear either way.
Glossary
Fourteen terms worth knowing cold
- Address
- The public string you share to receive funds, derived one-way from a public key. Safe to publish.
- Block
- A bundle of transactions plus the hash of the previous block, which is what links the chain together.
- Confirmation
- Each additional block built on top of the one containing your transaction, making reversal exponentially harder.
- Consensus mechanism
- The rule set deciding whose next block the network accepts — proof of work or proof of stake in almost all cases.
- Cost basis
- What you originally paid for an asset, including fees. Needed to calculate gain or loss when you dispose of it.
- Custodial
- Someone else holds your private keys. Your balance is a claim on that company rather than a position on the ledger.
- Gas / network fee
- Payment to the network for including your transaction. Set by congestion, not by the amount being sent.
- Halving
- Bitcoin's roughly four-yearly 50% cut to the block subsidy, throttling new issuance toward the 21 million ceiling.
- Hash
- A fixed-length fingerprint of any data. Deterministic, one-way, and wildly sensitive to the smallest input change.
- Private key
- The secret number that authorises spending. Whoever holds it controls the funds — there is no other layer of ownership.
- Seed phrase
- 12 or 24 words that regenerate every key in a wallet. Functionally identical to the money itself.
- Slashing
- Destruction of part of a proof-of-stake validator's collateral as a penalty for misbehaviour or serious downtime.
- Smart contract
- Code deployed to a blockchain that executes automatically. It does exactly what it says — including its bugs.
- Stablecoin
- A token designed to hold a fixed value, usually one dollar, backed by reserves the issuer claims to hold.
References
Market figures and regulatory facts are dated August 2026 and will move. Check primary sources before relying on any number.
- FBI, "Cryptocurrency and AI Scams Bilk Americans of Billions", April 2026 — summary of the 2025 Internet Crime Report.
- FBI IC3, 2025 Internet Crime Report (PDF) — complaint volumes, loss totals and fraud categories.
- TheStreet, Bitcoin price, 12 August 2026 — price, market cap, dominance and all-time-high reference.
- CoinGecko, Global cryptocurrency market cap charts — total market value, stablecoin share, assets tracked.
- Arnold & Porter, "Clarifying the CLARITY Act" — how the bill splits digital commodities, investment contract assets and payment stablecoins.
- Everstake, CLARITY Act and GENIUS Act: staking and DeFi — GENIUS Act signing date, reserve requirements and yield prohibition.
- Datawallet, "CLARITY Act Explained: SEC and CFTC Crypto Rules in 2026" — committee votes and rulemaking timelines.
- H&R Block, "What Is Form 1099-DA?" — proceeds-only first year and the cost-basis phase-in.
- CoinTracking, Form 1099-DA guide — covered vs noncovered assets and the 2025–2027 reporting timeline.
- Nasdaq, "2 cryptocurrency tax rule changes going into effect in 2026" — IRS Notice 2014-21 and per-wallet basis tracking.
- CoinLaw, Crypto adoption by country, 2026 — global ownership estimates and stablecoin settlement share.
- SolCard, "How Many People Own Crypto?" — why ownership estimates range from 560M to 741M.
- Fidelity, "What is a stablecoin?" — stablecoin types and de-pegging history.
- 3Blue1Brown, "But how does bitcoin actually work?" — written companion to the video in Module 1.