Draw a design that appeals to you on the paper. Fill it in with the mosaic tiles or beads until you have an image you like. Set that aside.
Mix the stepping stone mix with water in the bucket until you have a thick, mud-like paste. If you're using Portland cement, mix one part cement with three parts sand and enough water to make a thick paste. If the paste is too thick and sturdy, it won't work. If it's too runny, add more cement mix.
Scoop the cement mixture into the mold, pushing it and smoothing it down with the putty knife. Cut a piece of chicken wire to fit into the mold to strengthen the stone, if you'd like. Push the chicken wire into the mold once it's halfway full, then continue to smooth cement on top until the mold is full.
Shake the mold gently to evenly distribute all the cement and get rid of any air bubbles. Bubbles in the stone will weaken it, making it more likely to crack.
Transfer the mosaic tiles or beads or marbles to the stepping stone while the cement is still wet. Lay each tile on the stone first, then gently push down on the tiles to firmly embed them into the concrete. Instead of the tiles or marbles, you can also carve an image into the wet cement or write a word or phrase. Let the stone dry for at least 48 hours.
Remove the stone from the plastic mold. It should easily slide out if it's completely dry. Clean any rough spots from the stone with a sponge. You may need to hammer away any particularly large rough spots.