The ear has two very important functions for humans: hearing and balance.  

The structure of the ear

Human Ear

The human ear is divided into 3 parts--the external, middle and inner ear.

• The outer ear - this is the visible part of the ear. Its shape helps to collect sound waves.

• The middle ear - separated from the outer ear by the eardrum, the middle ear contains tiny bones (called the ossicles). These amplify the sound waves and pass them along to the cochlea.

• The inner ear - sound waves are changed into electrical impulses and sent to the brain. The sense organ of balance is located here, too. This is located inside the skull and is the most complex part of the ear.

When sound waves hit the outer ear, they travel through the ear canal and make the ear drum vibrate. The three small bones carry the vibration to the cochlea. Tiny hairs in the cochlea convert the vibrations of sound into neural messages that are passed to the brain through the auditory (cochlear) nerve. 

Reference:

"Ears Explained," Better Health Channel. Reviewed February 2006, Accessed: January 17, 2007.