Stencilling can be a fun effect to use on cakes, but the stencils themselves can get expensive. It's also hard to find the exact size and pattern that you're looking for, especially if it's a custom design.
Making your own stencils isn't difficult, but it's something that you have to do very carefully. If you're not good at working with extremely sharp knives and you tend to chop yourself up, this might not be the project for you.
Or you can buy a machine that cuts them for you, which is generally going to be a huge waste of money unless you use it for a lot more than that.
I made a set of stencils for the chrysanthemum cake that I made recently. This type of pattern is pretty common, so I might have been able to shop around and find something similar, but I needed specific sizes.
stencil plastic (available at craft stores) and an exacto knife and did them freehand so that they would all be slightly different. For the cutting board I used the mat that I have for cutting out quilting fabrics. Don't do this on a counter or a regular cutting board. You'll either ruin the cutting surface or your knife, so if you're going to be cutting a lot of stencils it's worth buying a self-healing cutting mat that's designed for the purpose.
The one thing to remember when you're cutting stencils is that you should NEVER put your non-cutting hand directly in front of the path the knife would take if you slipped. You don't want an exacto blade making friends with your fingers.
If you have a machine like the Cricut that will cut out stencils you can also use that, of course. You just have to find the right pattern to put in, but there are programs that can do that for you.
To store the stencils, put them between two pieces of stiff cardboard so that they won't get smashed and bent and put all your work to waste!