Circles and triangles work well, but you can experiment with other shapes, too. Clip them to the leaves of a plant, preferably one with large leaves. Either an indoor or an outdoor plant will do. Be very careful not to damage the plant. Leave one paper cutout on for 1 day, a second on for 2 days, and a third on for a week.
Plants use sunlight to turn carbon dioxide from the air, and water into food.
Plants need all of these to remain healthy. When the plant gets enough of these things, it produces a simple sugar, which it uses immediately or stores in a converted form of starch. We don't know exactly how this happens. But we do know that chlorophyll, the green substance in plants, helps it to occur.