In the space of fifty years, Earth changed from a planet on cusp of a challenging future to a world a breath away from lifelessness and plunged into an apocalyptic time of ecological disaster, global warfare and the meltdown of human civilization. This is the time of the Maelstrom.
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