I will make a leap of faith here that you are not asking a homework question.
Check this out
Vibration
Basically as, say, a guitar string vibrates, it causes small pressure waves in the air around it. Simplifying a bit, each back and forth movement of the string causes a small pressure wave so you are talking
lots of waves. The pressure waves enter our ears which react to the pressure waves and send nerve signals to the brain which interprets them for us.
You might also do a search on ear function or hearing. Try
The Human Ear