The brain is a very complicated chunk of stuff, with billions of individually simple neurons combining to give rise to very complex behaviour. This interactive video does a wonderful job of describing how it all works.
Created by Nicky Case, it's part-game, part-video. He guides you through almost as if he's there with you, and depending on what you click you'll learn something different each time. In fact, it's worth spending a little with it if you're going to get the most out of it.
He's made the whole lot available under Creative Commons, too, so if you like it you can download the code, re-use it, or maybe even use it to teach other people. Whatever, it's well worth a look.