Chaos Domain is a game about shooting bad people in the face. Apart from that, it is also a run and gun platformer, powered by Unreal Engine. The game is highly influenced by games from 8-bit and 16-bit era, including Contra/Probotector series, as well as titles like Abuse and Doom Troopers.
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