Not as hard as it sounds.
First of all you have to clean the rock.
Use some watered down white paint to ass a smooth layer and color and let it dry.
You need a “Splendid Blender” pen from Chartpak. Don’t try any other blender pens they don’t have the identical chemical composition, and will not work.
Make a copy of the image with a laser printer, Ink jet copies can not be used.
Place the paper with face down on the rock you plan to use.
Rub the pen over the image, while you keep the paper with the image in place. Be very careful if the papers moves you will end up with a blurry image. Apply pressure until the image is transferred.
Read more details: Playing With Rocks