Capture is the process by which payments are secured once the payment has been authorized. In order for a payment process to be complete when a credit or debit card is being used as the method of payment, the card must first be authorized. This step of authorization takes seconds and will allow the merchant to know that there are sufficient funds to complete the transaction.
When using a credit or debit card as a payment method, the money will not leave the account instantly, but instead will be reserved for the transaction that has just been completed. Once a payment has been captured, your internet banking statement will show the amount that was captured for the purchase as a pending credit/ debit transaction and the funds in the bank will not be available to spend elsewhere.