Use YOUR ARROW KEYS to move and jump and aim and shoot with YOUR MOUSE. Be sure not to walk into fires, fire is bad for you. Some zombies can hang on to you and slowly eat you up, that is also bad for you.
The object of this game is to survive in a hostile word and kill as many zombies as you can.
Even so, your PSP is not a brick. You can easily turn it into one, however, by failing to treat it with care. It's a little too big to be a paperweight, but it would make a fantastic doorstop, as you'd expect at its high price. If you want a doorstop, go to the hardware store and buy one. If you want your PSP to work as a PSP, treat it with respect.