First sound waves enter through the outer ear also called the pinna. The waves come into the ear canal, which ends at the eardrum. The sound causes the eardrum to vibrate which then makes the malleus hammer against the incus. The incus passes the sound waves to the stapes, which transmits the wave information to the entrance of the inner ear called the oval window. This process changes the wave vibrations from low pressure to high pressure so they can be detected by the fluid filled inner ear.
The movement of the oval window transmits the waves through the fluid of your inner ear into the fluid filled cochlea. It then spirals through the cochlea. Next it has to travel through the Corti, which is a membrane with thousands of sensory hair cells attached. Each hair cell contains a bundle of tiny sensory hairs which emerge from the cell. Resting on top of these hairs is a second membrane. When the waves move the fluid in your cochlea, the first membrane vibrates, pushing the hairs against the second membrane. This changes the waves into nerve signals. These travel along the cochlear nerve to your brain. Your brain then pin points the sound. That is why we as humans can here!