Commandos: Behind Enemy Lines is a real-time tactics game set in World War II that puts you in command of a small squad of elite troopers. Send them behind enemy lines on a series of hazardous missions, and bring them back alive. Clever strategy has never been so furiously action-packed.
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