Spore prints can be made by simply leaving a mushroom gills-down on a piece of paper for several hours.
Fungi reproduce from spores.
In mushrooms, spores are released from the gills that form on the undersurface of the mushroom cap. Spores are so tiny they're difficult to see with the unaided eye, though if you take a mushroom into a dark room and shine a torch on it you can often see the falling spores reflecting the light. Another way of examining spores is by making a spore print. Cover with a basin or jar for 12 to 24 hours. The basin keeps the mushroom out of draughts of air, allowing the spores to fall straight on to the paper.