Buy Sonic the Hedgehog

If you do not have a Steam account, you will need to download the client from the official website, install it and then create your account. Once you are logged into your account, click on "Add game" in the bottom left corner and then on "Activate product on Steam". After a few clicks on "Next", you can finally enter your CD key, the game will automatically be added to your library and the download will begin.

More information on Steam

Once you have bought your game, you need to use your Game Code on the Playstation Network to download your game. To access the Playstation Network, you need a Playstation 3, a broadband connexion, a PSN account, and a storage device according to your console: Hard disk drive, memory card, or USB drive.