When you hit an obstacle, such as a wall, you type the names of items that will help you get past it. You control Maxwell as he traverses levels left-to-right.
This means you can solve problems in a number of different ways, using imaginative and ingenious solutions. What's surprising is the sheer number of items included in the game.
Scribblenauts is a series of puzzle games which you solve by typing the names of everyday objects so they appear in the game and let you progress.