Short describes something that is not as long as usual. If your childhood bed is too short for you, your feet will dangle over the edge, and if a school day is short, you'll get out early.
The adjective short describes things that aren't long when you measure them, or have a small distance from one end to another, like your short hair or the short walk to the library. A small amount of time can also be described as short, like a short chat with your mom. As a verb, short can describe cheating someone out of money or not paying what is owed, like a friend who shorts you when the lunch bill arrives.