A single confirmation means that the transaction has been included in a block on the blockchain. Subsequent confirmations refer to the number of blocks that have passed since a transaction was added to a coin’s blockchain. The higher the number of confirmations, the more irreversible the transaction. While buyers and sellers may agree to wait for only one confirmation, most people wait longer in order to ensure that the transaction cannot be reversed.
Each merchant must decide how many confirmations each coin needs. There is no magic number. However, there are certain widely known recommended practises. A basic rule of thumb is that 3 blocks is a decent safe medium ground, 6 confirmations is recommended for large transactions, and really large transactions may require even more transactions.
A new block is added to the Bitcoin network every 10 minutes. That means that after an unconfirmed transaction is put to the blockchain, there will be one confirmation every ten minutes. Then, following that initial block, each subsequent block adds one confirmation. As a result, one confirmation takes ten minutes, three takes a half hour, and so on.