1. Click on this link and continue to finish installing Steam https://steamcdn-a.akamaihd.net/client/installer/SteamSetup.exe

2. Run Steam and login or create an account

3. On the top left corner of the screen click on "Games" and select "Activate a product on Steam..."

4. Click "Next" until you see the input form. Fill in your code then click "Next"

5. Your game activation is completed. Your game is ready to download. Once it's finished you'll be able to play the game immediately. Have fun!