A wallet looks like a place to keep money. It has a balance, a receive button and a send button. So it is natural to imagine the bitcoin sitting somewhere inside the device.
Try a different picture. The network keeps the record of all the funds that can be spent. Your wallet helps you find yours and prove you are allowed to spend them. That difference explains why keys matter so much.
Receiving and spending are different permissions
Think about a parcel. Telling someone where to deliver it should not let them open everything in your house. Bitcoin also keeps receiving and spending separate. You share a receiving address so people can pay you. You keep your private keys secret. A private key is a secret number that lets you authorize spending.
An address tells a sender how to lock a payment so that your wallet can spend it later. The details vary by address type. In a common setup, one private key controls the funds. To spend them, your wallet makes a signature with that key. Sharing the address does not reveal that private key.
A signature proves permission without handing over the secret
Your wallet prepares a transaction and signs it with the required private keys. Other computers on the network can check the signature using public information. They never need your private key.
A signature does not hide the transaction. Bitcoin’s main transaction history is public. Addresses do not show a person’s name. But activity can still be linked to a real person. Proving a payment is allowed and keeping it private are two separate things.
A balance is a useful summary
Imagine you receive 30,000 satoshis, and later another 20,000. Your wallet might show a balance of 50,000 sats. But underneath that number are two separate pieces: one of 30,000 and one of 20,000. Each piece is called an output. Until it is spent, it is an unspent transaction output, or UTXO for short.
When you pay someone, your wallet picks which outputs to spend. Here is a simple example. Your wallet spends the whole 30,000-sat output. It sends 12,000 to the person you are paying. It pays a 1,000-sat fee to the miner. It returns the other 17,000 to you as change, in a new output your wallet controls. This fee is only an example, not a suggested rate. The old output is now used up. The transaction created new outputs in its place.
An exchange balance adds another relationship
A custodial service, such as an exchange where people buy and sell bitcoin, holds bitcoin for its customers. The balance it shows you is a record the service keeps for you. The service controls the keys to its bitcoin on the network and handles your withdrawal requests. Your account login is not a Bitcoin private key.
With self-custody, you hold the keys, so you control spending. You also become the one who must protect those keys and be able to recover them. A familiar-looking app, or the word “wallet,” does not tell you enough on its own. Always ask: who can sign the transaction?
Back to that broken phone
A broken phone does not remove your outputs from the network. They are still there. Whether you can spend them again depends on one thing: can you recover the required keys and wallet information? Many wallets use a recovery phrase, a list of words that can rebuild your keys. What you need to recover depends on the wallet and how it was set up.
Keep learning and experimenting separate from moving real money. You can understand every example on this page without entering a real key, sharing a recovery phrase or buying anything. Never share your recovery phrase with anyone.
Optional reading for this lesson
Continue your study
Reading for this lesson
Reference for the wallet roles described here.
Why public addresses do not make activity anonymous.