Lay a sheet or drop cloth either in your yard or garage on which to fill your mold. Stone-shaped molds in many styles can be found at your local home-improvement stores or garden shops.
Brace your mold on the ground, folding the sheet under the mold, if necessary, to make the open end flat.
Mix your concrete to the package specifications. The ratio of mix to water will vary from brand to brand, so be sure to carefully read the instructions. If you would like to have a color other than gray for your stones, add concrete dye to the water before you mix.
Pour the concrete into the mold, bouncing the mold slightly against the ground when it is full to remove any air bubbles in the mix.
Allow the concrete to set for two to three days before removing the "stone" from its mold and installing it in your yard.
Cut the top level of sod away with a small hand trowel or sod cutter from the place you wish to pour the stone. Give the hole an irregular outline to provide a more natural, stone-like appearance.
Blend your concrete according to the instructions on the package, adding concrete dye to the water if you wish to have a non-gray stone.
Fill the hole with the concrete. Gently, without stirring, prod the poured cement with a stick to get out any air bubbles.
Let the concrete set for around 15 minutes, depending on the moisture level of the mix, your ground and the air. It should be stiff enough to hold texture.
Crumple the newspaper and use it to dab rough patterns in the surface of the concrete. This mimics a stone's natural texture. Allow the stone to dry for two to three days before stepping on it.