If you receive a Gift Card by email it will contain details of who sent you the Gift Card, along with possibly a short message from them. The email will also contain the Gift Card Code. It is probably a good idea to print out this email for future reference. You can now redeem the Gift Card in two ways.
1. By clicking on the link contained within the email for this express purpose. This will take you to the Shop page. You will then have the opportunity to choose a product, then proceed to check out as normal and be sure to enter your Gift Card code in the apply coupon box and continue your checkout.
2. During the checkout process, on the same page that you select a payment method there will be a box to enter a Coupon Code. Enter the Gift Card Code here, and click the Apply Coupon button. The code will be validated and the amount deducted from your cart. You can then proceed with your check out as normal.