When a digital currency user makes a payment, this transaction is broadcast to the rest of the network. In order for the transaction to be recognized as valid by the rest of the network it must be confirmed by the miners (proof of work) or stakers/minters (proof of stake) who maintain it.
The more confirmations that a transaction receives the more confident other users can be that it is a genuine and not an attempt at fraud through aa double spending attack. For most transactions fraud is so unlikely that 1 confirmation, or even zero confirmations but sufficient time elapsed, is considered safe to accept a transaction as valid. For larger and more important transactions, however, more confirmations may be required.
Miners confirm transactions in blocks, which is where the term ‘blockchain’ comes from. The length of each block will depend on the rules of the network; Bitcoin, for example, has 10 minute block times. This means that it will take an average of 10 minutes for each confirmation of a Bitcoin transaction, although this will vary for each individual block.