So instead of cluttering up the Fallout 3 thread I decided to start another one:
So basically you can do whatever you can imagine. As you play you will pick up different items and you will learn how to use them as you go, but you can seriously do whatever you want, and if you cannot you simply can go and make your own level and then everyone on PSN can play the level that you designed and rate your level on many different levels. If you do not want to design and create your own levels and environments you can simply play through the game or play through any of the infinite number of levels that other people all around the world have designed. All the while doing whatever you want, and by this I mean if you want to knock over the other person playing with you do it, if you want to put a donkeys tail or a flower on someones face that you are playing with, do it, if you want to have a pumpkin as your head do it, if you want to play an underwater level you can find one, can't find one? Make one and then everyone else can play it to, want to play alone have at it, want to play with 4 people on one PS3 do it, want to play with people from across the world do it, want to go through the American Gladiators course level with your friends do it, is the course not exactly correct, could you make the level better? Do it, want to run through the Ninja Warrior level, do it......... Get the picture?
FULLY customizable EVERYTHING, if you can think it you can do it, it really is your own Little Big Planet, great game.