You can view 35mm slides by holding them up to a light source or by using a small personal viewer, but those methods pale in comparison when you can actually project the slides onto a screen or wall. While slide projectors may be hard to find these days -- unless you pick one up at a garage sale or through an online auction site -- you can try to make one at home.
Locate both a concave and a convex lens. Disassemble an old pair of binoculars, a telescope or an old camera lens to find the lenses. The concave lens will have at least one surface that curves inward, while the convex lens will have at least one surface that curves out.
Take a paper towel cardboard tube and cut it in half, lengthways down the entire tube, creating two semicircle tubes. You will only need to use one half of the tube, so discard the other half.
Attach the tube to the small piece of plywood with drawing pins inserted through the bottom of the tube. Keep the open side of the piece of tube facing upwards so you can insert the slide and lenses. Cut a small slit 1 inch from the back end of the tube. Do not cut the slit the entire depth of the tube, as you want it to support the slide.
Place the flashlight behind the tube, with the light directed towards the slide.
Place a slide into the holding slit you cut.
Position the convex lens in front of the slide. Position the concave lens with flat side closest to the convex lens. Adjust the distance between the two lenses until the image from the slide is in focus on the wall or screen. Use a pen and mark on the tube the position for the two lenses.
Cut a slit into the cardboard tube to support the two lenses. Insert the lenses into the tube to complete your projector.