The important parts of the eye are shown in the cross-section view.  The conjunctiva is the delicate membrane which lines the inside of the eyelids and the outer surface of the eye, except for the cornea. The sclera is the white, tough covering of the eye.

The iris is the colored part that contracts and expands in order to allow the pupil to let just the right amount of light into the eye.  The pupil is an opening just like the shutter of a camera that lets light enter the eye.  Light passes through the lens and is focused onto the retina at the back of the eye.  Nerve fibers in the retina carry light and images to the brain through the optic nerve.