1. In order to activate your Gift Card on Steam, first you need to install the Steam Client Application. You can download it here.

2. After you download and launch the app, sign in with your Steam logins, and select ‘View my wallet’ from the drop down menu as showed in the picture below.

3. After you are taken to the Wallet page, select “Redeem a Steam Gift Card or Wallet Code”

4. Copy the Activation Key and paste it in the Steam Wallet Code field, then click ‘Continue’.