Steam
How to activate a Steam Gift Card?
Log in to your Steam account;
First, click your account name in the top right of the site, then click Account details;
Click Add Funds to your Steam Wallet;
Click Redeem a Steam Wallet Code;
Enter the Steam Gift Card code that you received in your email;
Click Continue. Note that if you have never used Steam Wallet credit on your account before, you may be prompted to enter your current address in order to determine the correct currency.