Steam is a multiplayer matchmaking service originally available on the PC and Mac. With the release of "Portal 2," Steam became available on the PS3. At the time of publication, "Portal 2" is the only way to get Steam on the PS3. The PS3 version of Steam includes all of the features found on the computer versions, including access to friends list, Steam Cloud and achievements. The most noteworthy addition to Steam on the PS3 is the ability to play cross-platform between all Steam platforms. A free PlayStation Network account is required to access Steam.
Insert "Portal 2" or another Steam supported game into the PS3.
Press the "Select" button on the game's main menu to open the Steam overlay. If you are not already signed into a PSN account, you will be prompted to do so before you can continue. If you don't have a PSN account, select "Sign up for a PlayStation Network" account and follow the instructions on-screen to complete the registration process.
Enter the email address and password associated with your Steam account using the on-screen keyboard and select "Sign In." If you don't have a Steam account, select "New Account" and follow the instructions on-screen to complete the registration process. After creating the account, you will be signed in automatically.