The pupil is the black part of the eye. light passes through the pupil. The iris is the muscle that makes the pupil smaller or bigger to control how much light gets through.
The lens focuses the light on the back of the eye. The lens is attached to the ciliary muscle. the ciliary muscle changes the shape of the lens to focus on something that is close to the eye of far away from the eye.
From the ciliary, the light goes to the back of the eyeball the retina. The lens focuses the light onto the retina. The retina has millions of light-sensitive cells called rods and cones. With the rod cell you can see black and white and with the cone cell, you can see color.