Instructions
Connect the first PS3 controller to the PS3 console's USB port using the controller charge cable. Press the "Home" button on the first controller to sync it with the console, designating it as "player one." Remove the charge cable from the PS3 controller.
Connect the second PS3 controller to the PS3 console in the same manner. Press the "Home" button to sync the controller, designating it as "player two." Remove the charge cable from the controller.
Connect and sync the remaining controllers until all four players have been synced with the console.
Launch a game from the PS3 XMB menu to begin playing with four players.