For most credit card purchases, the transaction is broken up into two parts.
First we authorize the order total on your credit card when you checkout. An authorization (or pending charge) is a temporary hold on funds within your account.
Once your order is shipped, we charge your card for the relevant total. This will mean that your bank will sometimes show the charge as a second transaction, but the bank will remove the pending authorization usually within 2-5 business days.
Similarly, if your order is cancelled, the pending authorization may take 2-5 business days to drop off your bank statement, depending on your bank.