Instructions
Power on your Sony PlayStation and wait for the startup menu to appear.
Press the "Right" directional arrow button until you reach the "PlayStation Network" menu, then move down and select "PlayStation Store." This connects you to the online store for your PS3.
Select "Game Demos." This entire section provides hundreds of different games available for free.
Choose the game you want and select "Purchase," then "Proceed to checkout." Because the game is free you do not need to provide any credit card information. Select "Begin Download" and the game downloads to your PlayStation 3.
Return to the main menu (there is an "Exit" option in the PS3 store). Push the left arrow button until you reach "Games." Move down and select the game you just downloaded. This installs the game onto the system. When the game has finished installing highlight the game and press "X." The free game now begins to play.