Confirmations are when your Bitcoin transaction is included in a block, cementing its place on the blockchain and making it irreversible.
An example of this is when you want to withdraw your newly purchased Bitcoin from a centralized exchange to your own Bitcoin wallet for safekeeping.
As this transaction from the exchange to your bitcoin address is broadcast to the network, the nodes will verify that the bitcoin you wish to withdraw is indeed available in the exchange’s bitcoin wallet and has not been double spent.
Once verified, the transaction will be added to the next batch/block of transactions and miners will then process that block. This processing of the block is called confirmation.
Every 10 minutes, new batches of transactions are processed and added, which will include all previous transaction history from the Bitcoin blockchain. Thus every 10 minutes, an additional confirmation is added.
A general rule is that 6 confirmations are enough to make the transaction permanent, but sometimes even 2 confirmations are enough.