If you have purchased a game that requires Steam, please following these instructions to activate the game. (please note depending on your operating system, these images may vary slightly)
1) Click to your Account (top navigation bar).
2) Go to MY GAMES and find the game in the list. On the right side click on Steam.
3) The screen will show you the Steam code required to activate a game on Steam. Copy it.
4) Launch Steam. If you don't have Steam installed on your computer, you may find the installer HERE.
5) On launch of Steam and this is your first time using Steam, it will ask you to login or create a new account.
6) Once you are logged into Steam, click on + ADD A GAME... in the lower left side of the Steam screen.
7) Then select Activate a Product on Steam.
8) Enter the Steam code by pasting the key you copied in Step 3.
9) Follow the on-screen instructions from that point to begin downloading and installing your Steam game!