When you look at your eyes in the mirror, you're only seeing a part of them. The whole eye is shaped like a round ball, most of it is inside your head and protected by your skull. Your eyelids and eyelashes protect your eyes too. Your eyelids make it possible for you to close your eyes, shutting out the light when you are tired. Closing your eyes makes it easier for you to go to sleep.
Light strikes something and bounces off.
This reflected light, the light that bounces off the thing you are looking at, travels into your eyes through the pupil. As the light enters the eye, it passes through the lens. The lens helps to take out the fuzzy look of the thing you are looking at, focusing the image. When the upside down image shines on the back of your eye, it strikes the retina. The retina contains the optic nerve that sends the message of what you are looking at to the brain.