In a desperate war for Earth’s survival, against an unrelenting enemy, the only way to defeat them is to become one of them. Armed with advanced weaponry and vehicles and aided by an elite squad of marines, you take the battle to the heart of the Strogg home planet and become earth’s only hope for victory.Go to: http://store.steampowered.com/ and download STEAM client
Click “Install Steam” (from the upper right corner)
Install and start application, login with your Account name and Password (create one if you don’t have).
Please follow these instructions to activate a new retail purchase on Steam:
Launch Steam and log into your Steam account.
Click the Games Menu.
Choose Activate a Product on Steam…
Follow the onscreen instructions to complete the process.
After successful code verification go to the “MY GAMES” tab and start downloading.