26 years after a fatal accident in Chernobyl Nuclear Power Plant that covered half of the Europe in clouds of radioactive smoke, a large group of terrorists took over the area, trying to steal all the remaining radioactive waste - and use it.
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