The outer ear collects sound waves. The sound waves travel from the outer ear to the middle ear. The eardrum changes the sound waves into vibrations. The hammer, anvil, and stirrup bones vibrate. The sound moves to the inner ear. The sound enters the liquid-filled cochlea. The cochlea vibrates. Small hairs in the cochlea move. Nerve signals are created. The brain understands the nerve signals as sound. 
How does the human auditory system work?