The best-selling first-person action game of all time gets even bigger with more epic new multiplayer content! The Modern Warfare 2 Resurgence Pack delivers five incredible new multiplayer maps. Take the action to exciting new locations, then battle across legendary landscapes from Call of Duty 4: Modern Warfare.
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