You think Tower Defense games are all about building? You thought wrong. Sanctum is not your average Tower Defense title. When the havoc starts, you get to join the fray! As one of the world’s first First Person Shooter - Tower Defense games, Sanctum has taken the best of both worlds to deliver an epic, one-of-a-kind experience.
Open the Steam client, login and locate the Games tab on the top menu. Click this and then select “Activate a Product on Steam…”
Enter your unique code that's displayed on the 'Orders' page of CDKeys.com and follow the prompts to activate.
Your game is now viewable in the “Library” tab and is available to download/install when you’re ready. You can find additional support for the Steam client here: https://help.steampowered.com/en/wizard/HelpWithSteam