Make a pinhole camera
Empty Pringles Tubes with lids, Gaffer tape, Tin foil, Thumb tack or simular, Sharp knife and possibly white tissue paper.
Your eyes, and the eyes of many other animals and insects, work the same way as a pinhole camera. Building your own pinhole camera will help you understand how this works.
Take an empty Pringles Potato Chip can and wipe out the inside so it is clean. Cut off the bottom two inches of the can with a sharp knife (you might need your mom or dad to help with this part).
The short piece has a metal bottom. Use a thumbtack to make a tiny hole in the center of the metal bottom. That's where the light will come in: it's like the black pupil in the center of your eye.
You're going to use the plastic lid as a screen, like the movie screen that the picture projects on to, or like the retina inside your eye. If the plastic lid on your can is translucent (light comes through but you can't see through it), you're good to go. If it's transparent (you can see through it), then you should tape a piece of wax paper or tissue paper to the lid.
Put the lid on the short piece, to make a short Pringles can. Now put the longer piece on top of the lid, so you have an open Pringles can with the lid blocking the middle of it. Tape it all together.
You need to keep all the light out of your camera, so roll your tube in some tinfoil twice around, and tape the foil on. Tuck the end of the foil over the open end of the tube. (You can also add a foam soda can holder over the open end of the can, to help keep light out.)
Take your camera outside on a sunny day. Hold the open end of the camera up to your eye. Make the inside of the tube as dark as possible. Can you see an upside-down picture of the outside on your plastic screen? Your eye also makes upside-down pictures on your retina, but your brain learns to flip the pictures right-side-up without your even thinking about it.
There is also an alternative design using a shoebox (or similar) attached.