Try this: look in a mirror. Notice the parts of your eye. There are eyelashes. There is an eyelid that opens and closes. These keep dust and dirt out of the eye. Blinking the eyelid helps to keep the eye moist. The eyelid helps protect the eye, too. If something moves quickly toward your eye, the eyelid closes to protect it.
There's the white part of your eye. You can see blood vessels in it. Then there's the colored part. Inside it, there's a black circle. Try turning on a light overhead. What happens to the black circle? Did it get smaller?
People's eyes are amazing. The black circle in the center of your eye is called the pupil. It is an opening that lets light in. In a dark room, the pupil opens wider. The black part of the eye looks bigger. Then in bright light, the pupil gets smaller to let in less light.