Scribblenauts is a puzzle game similar to many others where your character must collect an item, in this case a star, to complete the level and move on to the next. Where Scribblenauts gets interesting is that you can use just about anything you can think of to help you get that star. Just write in a word with the stylus, the game has a vocabulary of over 20,000, and that item will come to life.
Need to get a star down from a tree? Why not use a wood chipper, or a wood chuck, or an axe, or … well, you get the picture. Solving puzzles was never this fun until you could use 22,802 possible items in a game.