Confirmations are blocks that have been generated after the block that contains the transaction in question. At least 6 confirmations are required after a Bitcoin transaction before it is officially added to the chain. Since Bitcoin has 10 minute block times, it takes 10 minutes on average to add a block. You therefore need to wait for about an hour to add a transaction. Increasingly, services are reducing the number of required confirmations and honoring transactions when they first appear on the network. There is some risk here, but compared to credit card transactions it is hardly worth mentioning.