Why do Computers Use Binary?

Three things that I learned is that binary is a system for representing numbers using only the digits 1 and 0. Also I learned that computers have a computer jack that can make you listen to music on your phone. Analog Signal is a signal that's proportional to the value it presents. I still don't understand how the sound from the computer goes to the headphones and how numbers would make the sound go threw. I would like to know more about how the sound can get louder.