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.
You could also try a Silhouette Cameo vinyl cutting machine. You can get designs for less than $1 each and cut them out of vinyl on your machine to use as stencils. But of course, the machine itself is fairly expensive.
Or you could try this super inexpensive method of making your own DIY stencil: https://www.youtube.com/watch?v=Llz1xMhDwqk
This is another inexpensive method to make a stencil: https://salvagedinspirations.com/how-to-make-a-stencil-no-costly-gadgets-required/
This is another good tutorial: https://www.thesprucecrafts.com/how-to-cut-a-stencil-2579185