Track the Bad Guys, be brutal and smart in your planning, and eliminate them one by one. But bear this in mind: each criminal’s death has to look like an accident. In each level, you’ll have the chance to splatter and destroy the Bad Guy using various weapons and traps.
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