Rockstar Games is the developer and publisher of the "Grand Theft Auto" series. All of the PC versions of the "GTA" games, including "Grand Theft Auto: San Andreas," are sold through the Steam delivery content by Valve Corporation. If you want to play "San Andreas" on the PC, you must purchase it and download it through Steam.
Launch Steam from your PC, and search for "San Andreas" via the search bar. Alternatively, you can log on to http://store.steampowered.com.
Click "Add to Cart," and select "Purchase for Myself."
Fill in your financial information, and click "Purchase." The game will automatically download after purchase.