Instructions
Insert batteries into the bottom of your keyboard and mouse (if they are wireless as opposed to wired devices).
Press the "Connect" button on your keyboard and mouse (if they are wireless and are designed specifically to work with the PlayStation 3). Just like PlayStation 3 controllers and headsets, the system's official keyboard and mouse have a circular "PS" connected button located atop the hardware. Pressing the button connects it with your system, allowing you to use them during games.
Plug your keyboard's USB cable into the front of your console (for wired devices). Do the same with the USB cable that is attached to your mouse. You can use either USB input on the front of the PlayStation 3 with your wired keyboard and mouse. Any keyboard and mouse you can use on a computer will work with the PlayStation 3. The only buttons that won't work are "Media" keys, like the kind designed to open a program or eject the disc tray on a computer.