When does a Bitcoin transaction get its first confirmation?

Detailed explanation

An unconfirmed transaction can be relayed by nodes and stored in mempools but is not yet part of the blockchain. Once included in a valid block belonging to the current best validated chain, it receives its first confirmation. The next block on that chain increases the count to two, and so on.

More confirmations do not mean a central authority adds signatures. They mean more proof of work has been built on the block and its successors. To remove the transaction or replace it with a conflicting one, an attacker would have to create a competing history that overtakes the authoritative chain. Each additional block generally makes this harder and more expensive.

Confirmations are therefore a growing security indicator, not mathematically absolute finality. The appropriate number depends on amount, risk and use case. Small payments may be treated differently from very large or fraud-prone transfers. A transaction visible in the mempool, by contrast, still has zero confirmations.