A CPU- or Central Processing Unit, is a very fast computer chip, containing millions of transistors. It is like the "brain" of a computer. Just like your brain takes care of seeing things, feeling them, understanding instructions, and figuring out what to do with the information your brain gets, the CPU, processes all the information coming in and sends commands out to do things like "print", or "show the image on the monitor" or connect to the Internet.

There is one important difference between your brain and a CPU (besides that yours is bigger and smarter). Your brain can make decisions after getting information in to it. A CPU can not make decisions. Your brain evaluates the information you give it and tries to figure out the best thing to do. Sometimes we learn that what we decided was the right thing to do and sometimes we learn that our decision was the wrong thing to do. CPUs just do what they are told.