Join and Install Steam
The first step to redeeming a Steam key if you have not already done so is to create a Steam account and download the Steam client. You can do these things at the following pages:
Redeeming your Steam key
Follow these instructions to redeem your Steam key:
Locate your Steam key. You should have received this via email after making your purchase.
Within the Steam client, locate the “+Add a Game” link at the bottom left of the screen. Click this link and then select the “Activate a Product on Steam…” option.
Enter your Steam key into the “Product Activation” popup that appears.
Once you have activated your Steam key, your game should appear in your Steam library which can be accessed by clicking the Library tab at the top of your screen. Click on the game that you have activated and you should now be able to install and play your game.
Enjoy!