Sound is really air pressure waves. Hearing begins when those waves enter the outer ear and are sent down the ear canal, a one inch passageway lined with tiny hairs and small glands that produce earwax.
Sound waves hit the eardrum which engages the Middle Ear which is composed of the eardrum and three small bones, known commonly as the hammer, the anvil, and the stirrup. When sound waves hit the eardrum, it vibrates and, in turn, moves the hammer. The hammer moves the anvil, which moves the stirrup, transmitting the vibrations into the inner ear.
The inner ear consists of the cochlea and the vestibular (balance) system. The cochlea converts sound waves into chemical electric nerve impulses that travel to the brain via the movement of tiny hair cells. This is an amazingly complex interaction, no computer yet devised could replicate it for even a second. It is the brain that allows you to hear.
The following is an informational video my MED-EL which explains this concept.