At the time your order is placed, a pending hold is placed on the amount of your order. You are not actually charged until your items are ship. If your order has been canceled before shipping, you will not be charged. You may still see a pending hold on your account, which will "drop off" within a few days, depending on your bank.
In the case of debit cards, authorization holds can fall off the account rendering the balance available again. This can take anywhere from 1 to 8 business days after the transaction date, depending on the bank's policy.
In the case of credit cards, holds may last as long as thirty days, depending on the issuing bank.