Call of Duty: Black Ops is the seventh main Call of Duty game and the sequel to Call of Duty: World at War. The game differs from most previous installments, which would involve a usual three-country campaign, while Call of Duty: Black Ops features two playable countries (Russia and the USA) but only has an American campaign. Several new features are also introduced, such as dive-to-prone and the available use of a flashlight on certain weapons. Furthermore, the campaign's playable characters now speak while being controlled by the player.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.