In order to activate your game, you please follow the steps below:

1.) Download and install Steam from here: http://store.steampowered.com/about/
2.) Create a new account or log in to an existing one.
3.) Once you have logged into Steam, click on “Games” in the top toolbar.
4.) Select “Activate a Product on Steam…” and follow the on-screen instructions.
5.) Enter your product code when prompted to.

After completing all of the above steps, your game should begin downloading and will be available under the “LIBRARY” section of Steam.