Simply add your products to your cart. When you are ready to pay, click the Checkout button and choose "Gift Certificate" for the payment method. You will then be asked to enter your Gift Certificate ID number. If your gift certificate amount is not large enough to cover the complete order total, the cart will re-calculate the remainder and you can then choose to pay the remainder via Credit Card or PayPal. Each unique Gift Cert ID may be used only 1 time (even if the amount is not totally used up the first time).