One Transaction, End to End
Most explanations of Bitcoin describe the parts. This one follows a single payment through all of them, in order, so you can see how the pieces connect. Meet Ana, who owes her friend Luis 0.005 BTC — about the price of a nice dinner. Everything below is what actually happens when she pays him.
No special equipment is involved. Ana has a wallet app on her phone; Luis has one on his. Watch for the four words that carry the whole story: keys, mempool, block, confirmation.
Step 1: Luis gives Ana an address
Luis taps "receive" in his wallet, and it shows an address: a long string of letters and numbers, often displayed as a QR code. The address was derived from Luis’s public key, which was derived from his private key — a secret his wallet generated when he set it up and which never leaves his device.
Sharing the address is safe. It is a destination, not a key. Anyone who knows it can watch payments arrive, but only Luis’s private key can spend what lands there. Ana scans the QR code, which saves her from typing forty characters by hand — the most common source of expensive mistakes.
Step 2: Ana’s wallet builds and signs the payment
Ana enters 0.005 BTC. Her wallet quietly assembles a transaction: it selects some bitcoin she received earlier (her spendable balance), directs 0.005 of it to Luis’s address, sends any leftover back to a new address of her own as change, and adds a small fee for the miners.
Then her wallet signs the transaction with her private key. The signature is a mathematical proof that the owner of those funds authorised this exact payment — to this address, for this amount. Change a single character of the destination and the signature no longer matches. Ana’s private key itself is never sent anywhere; only the proof travels.
Step 3: The payment waits in the mempool
Ana taps send. Her wallet broadcasts the signed transaction to the network, and within seconds it sits in the mempool — the shared waiting room of payments not yet written into the record. Luis’s wallet can already see it and may show the payment as "pending."
Pending is not paid. A transaction in the mempool can still be replaced or dropped, which is why shops and exchanges wait. Miners assembling the next block generally reach first for the transactions offering the highest fees per byte, so Ana’s fee choice quietly decides how long this step lasts: generous fee, busy hour, first in line; tiny fee, possibly a long wait.
Step 4: A miner writes it into a block
Roughly every ten minutes, one miner somewhere in the world wins the proof-of-work contest and publishes a new block — a batch of a few thousand transactions, Ana’s among them. Every node on the network checks the block and, finding it valid, adds it to its copy of the chain.
Ana’s payment now has one confirmation. It is in the permanent record, signed, timestamped, and visible to anyone who cares to look — though the record shows addresses and amounts, not names. Luis’s wallet updates: the dinner debt is settling.
Step 5: Confirmations make it boring — and final
Each new block stacked on top of Ana’s block is another confirmation. To undo her payment, someone would have to redo the proof of work for her block and every block after it, faster than the rest of the world combined — a feat that grows more unrealistic with every block. Six confirmations, about an hour, is the traditional "consider it settled" mark, though small payments are often accepted after one.
Luis can now spend the 0.005 BTC with his own private key, exactly as Ana spent hers. The whole journey — address, signature, mempool, block, confirmations — took minutes, involved no company, and cannot be charged back. That combination is the entire invention, seen at walking pace.
Every Bitcoin payment, from a dinner debt to an exchange moving millions, takes this same five-step road. When news or salespeople make Bitcoin sound like magic, walk the payment through the steps in your head. Magic rarely survives an itinerary.
Written by Robert King for Bitcoin in 15 Minutes. Educational only — not financial advice. Spotted an error? Tell me and I will fix it.