Please follow these steps:
1) During the checkout process select a "Payment Type" of "Gift Certificate"
2) A new "Add Certificate" section will appear. Paste in your gift certificate code and then click on the gold plus sign. You will then see confirmation that your gift certificate has been applied.
If the value of your gift certificate is less than the total amount of your order, you will be prompted for a payment method to cover the additional amount due.
If you still have trouble redeeming your gift certificate after following these instructions, please click here to open a help ticket.