Sound waves are collected by the outer ear and directed along the ear canal to the eardrum (tympanic membrane). The sound waves reach the ear drum and their impact vibrates this membrane, which in turn causes the vibratory motion of the three little bones (Malleus, Incus, Stapes) in the middle ear cavity. The smallest of these ossicles, the Stapes, fits into the oval window between the middle and inner ear. 

When the oval window vibrates, fluid within the inner ear transmits these vibrations into the cochlea, which is a snail-shaped structure within the inner ear cavity. The cochlea is the organ of hearing and consists of thousands of microscopic hair cells which are bent by the wave-like action of the fluid within it. The bending of these hairs sets off nerve impulses which are then passed though the auditory nerve to the hearing center in the brain. This center then translates these nerve impulses into sounds which the brain recognizes and decodes into meaning