Why Do Computers Use Binary?

During the video we watched during class I learned that computers use a signal to get sound from one place to the next like in headphones. The sound travels from one end end of the headphones to the other. The sound also beats on your eardrums causing you to hear the sound that is travelling through the signal. I learned how to fix a high binary number by just giving it a smaller range. I don't quite understand counting with large numbers through binary it didn't come to me right away. I also did not quite understand how adding numbers together works. I would like to know more about adding the binary numbers because it seems like something I might be able to use in the future.