The vibrations from the eardrum set the ossicles into motion. The ossicles are three tiny bones (smallest in the human body): Malleus (hammer), Incus (anvil) and Stapes (stirrup) which further amplify the sound.
The stapes attaches to the oval window that connects the middle ear to the inner ear. The Eustachian tube, which opens into the middle ear, is responsible for equalizing the pressure between the air outside the ear to that within the middle ear.
The sound waves enter the inner ear and then into a snail shaped organ called the cochlea. The cochlea is filled with a fluid that moves in response to the vibrations from the oval window. As the fluid moves, thousands of nerve endings are then set into motion. These nerve endings transform the vibrations into electrical impulses that then travel along the auditory nerve to the brain.