Steam Gift Card $20 US Activation Code

How to Redeem Steam Gift/Wallet Card

Log into your Steam account (or make one if you don't have one) and go to "Redeem a Steam Wallet Code"
In the resulting screen enter your code into the “Steam Wallet Code” field.
Click Continue.
Now you will have the amount of denomination of the gift card added to your Steam Wallet which is viewable in the upper right corner of Steam.