The ear is divided into three parts from the outside: the outer ear, middle ear, and inner ear. The outer ear extends from the entrance to the eardrum, and the middle ear extends behind the eardrum. Further inside the middle ear is a canal with fluid inside, called the inner ear. This is called the inner ear. The inner ear looks just like a snail.
Now, suppose a small bird makes a "beep-beep-beep" sound nearby. Its voice makes the air around it tremble, and that tremble enters our ears. It makes our eardrums shake. The vibration of the eardrum passes from the middle ear to the inner ear and further shakes the fluid in the inner ear. The shaking of the fluid passes to the sensory cells in the inner ear, which send signals to the brain, and this is how we hear the "beep-beep-beep" of a bird's call.