Download the IndyCar Pack to receive two routes at the world famous Indianapolis Motor Speedway Circuit plus receive the Dallara IndyCar and Indy500 Pace Car liveries for the Chevrolet Camaro SS and Corvette Z06 Centennial Edition.
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