If you're blessed with an awesome sister (or brother), you may receive one of those by email on your birthday: an Amazon gift card! This tutorial shows you how to add and redeem that gift card to your Amazon.com account. Click on the "Redeem now" button in the email. Unless you just logged into Amazon, you'll be required to enter your email address and password - that's to avoid seeing the gift card applied to the wrong account, on purpose or accidentally.
Skip to the next step if you received an email link, and clicking on it worked. If the redeem link in your email doesn't work, or if you only have the code for the card, you can go to this page on Amazon, and enter the "Claim Code" shown in the email message. Now click on the Apply to Your account button.
Either way, you should have landed on a page that looks like the one on your screenshot. If not, double-check for any typos in the claim code you entered and/or follow the error message's instructions. Otherwise, click on the Apply to Your Account button. You'll get a chance to add more than one gift card.
If everything went through, you'll get a "Your $123.45 gift card has been applied to your account" confirmation message. On the right of that page is a current total for all your gift cards' unused balance. If you received multiple Amazon gift cards, click on "Enter another gift card" on the left and keep going.
There is no expiration date on Amazon gift cards, so you don't have to spend all at once :) To actually redeem your gift card, just check out. On the final screen, where you actually place your order, your gift card balance will automatically be applied towards your order's total - no need to do anything else. Enjoy!