After you have installed the Steam Client, created a Steam account and logged into the Steam Client using that Steam account you can activate your games.
Once you have activated a game in a Steam account it cannot be activated in another Steam account, but you can login using the same Steam account on more than one computer then download the same game to each computer.
If you don't yet have Steam installed, or are using a device on which you don't run the Steam client, you can add the game to your Steam library through your web browser (after entering your Steam username and password) at the following page:
To activate a game in a Steam account using your Steam client program and then download, install and play the game:
- At the main Steam window:
- In the lower left corner of the Steam window, click on "+ ADD A GAME..." and then on "Activate a Product on Steam...":
- In the upper left corner of the Steam window (above STORE, LIBRARY, COMMUNITY) select the "Games, Activate a Product on Steam..." menu:
If you want to download the game now, click the "NEXT" button, otherwise click the "CANCEL" button.
Steam can optionally create shortcuts to play the game on your computer desktop or in the "Start" menu to make it easier for you to start the game.
If you would like Steam to create these shortcuts tick the check boxes, then click the "NEXT" button.
Steam will install the game into the folder shown, change this if required.
Once a game is downloaded and installed you can start it via your Steam Library of Games by selecting the game in the list then click the "PLAY" button:
Alternatively, if you created them during the download and install stage, you can use the game shortcuts on your computer desktop or in the "Start" menu to start the game.
If your game includes extra Downloadable Content, this article explains where you'll find it.