Take on the role of the captain of a troubled jumbo jet carrying infected passengers intent on bringing the plane out of the sky, or pit yourself against hundreds of zombies in the interior of a jumbo jet or even walk along the outside as you fight to regain control as one of the passengers.
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