Maybe it was the fact that people got to blow away Nazis. Maybe it was the sheer challenge of it all. For whatever reason, Wolfenstein 3D and Spear of Destiny, pioneered the first-person shooter genre and brought its legendary creators, id Software, worldwide notoriety and numerous awards.
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