To reedem your gift certificate, simply shop as normal and select 'Gift Certificate' as your payment choice at the checkout page. Enter in the gift certificate number and the pin that have been assigned to you.
If your total purchase exceeds your gift certificate balance, you may pay the difference by credit card. Click on the 'Add a second payment method' link (under the gift certificate form) and a credit card form will appear. The system will automatically assign the maximum amount to the gift certificate and the rest of the purchase total to the credit card.
Please note that gift certificates are not redeemable for cash.