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Blocks and transactions
A transaction moves bitcoin, and a block is a batch of them added to the chain about every 10 minutes.
- A transaction says which coins move to which address, signed with the owner's key.
- Miners bundle waiting transactions into a block, about every 10 minutes.
- Each block links to the one before it, so changing history means redoing the mining work for every block since.
When you send bitcoin, your wallet signs the payment with your private key and sends it out to the network. Nodes, the computers that keep Bitcoin's shared record, check the signature and that the coins haven't already been spent, then pass it on.
The payment waits in the mempool until a miner, one of the computers that build blocks, puts it in a block. Each block carries a fingerprint of the one before it. That links the blocks into a chain, which is why it is called the blockchain.
Once your payment is in a block, it has one confirmation. Every new block on top adds another. Many services treat six confirmations, about an hour, as final.
Want to go deeper?
Can I cancel a payment?
Not once it confirms. Bitcoin payments can't be reversed, so check the whole address and the amount before you send. While it is still waiting, some wallets let you replace it with a higher fee.
Is the blockchain public?
Yes. Anyone can look up every transaction and address on a block explorer such as mempool.space. Names are not recorded, but addresses can sometimes be linked to people, so treat every payment as public. More in Bitcoin privacy basics.
Should I send a test amount first?
For a new address or a large amount, yes. Send a small amount, wait for it to arrive, then send the rest. The extra fee is cheap insurance.