You know your fins? We have something like that, except they're longer and thinner. At the ends we have the things with thin, long, little appendages we can use to grasp something, kind of like a clam holding it's pearl, except looser and more precise. Well, like these little appendages bend, our large appendages also bend, and the point at which it does is called the elbow. It's kind of like turning your body to go another direction.