Make an exact drawing of your design on a piece on poster board you can buy at Walmart...make sure you leave 3 or 4 inches around your design...cut your design out with an small exacto blade so you can cut precisely...Whala!!!...its ready to use...if you are using different colors...you might consider making a separate stencil for each color...use a sponge brush to dab in paint slowly so you do not get drips underneath stencil!
Oh...just see one on here where they cut the same shape multiple times in a pattern...that is possible too!!!
My girlfriend makes them out of the flexible cutting mats from the dollar store. Being plastic, they are reusable for a long time.
I bought a Cricut machine and I can design and cut out virtually any design or wording I want. I love it.