Depends on what you want your stencil to do.
I've made large stencils of my address number in Illustrator, which could just as easily be done in Word. Make them as big as you want, then print them out in sections.
Use spray adhesive, contact cement (or old PVA glue that's been laying around ) glue the paper to cardboard, cut it out with a razor knife--leaving attachment lines (like a Cross across a '0' so the center doesn't just drop out.)
If you want to stencil something on a kayak, you could skip the cardboard step, cut it out of the paper, then use removable fixative spray to tack the paper to your kayak. Curved surfaces will require a work around.

For something more elaborate, take a look at Arts & Craft stencils, William Morris. Some of these patterns are for sale, some are very complex, but you could simplify them and make your own stencils. The basic idea is one stencil is for green leaves, another that you use after that has dried is for red, another for yellow, etc... as many as you want.

Tricks for stencils that I learned the hard way.
1. Don't use a lot of paint. Stenciling Arts & Crafts patterns uses a round brush that is almost dry. Load a little paint on the brush, poke it gently on a piece of scrap until it's almost dry then poke it straight down on your stencil (90 degrees from the wall, no brush strokes--because that'd just put it under the edge of your stencil). Remember the time that old professional painter or your dad said, "Paint it don't poke it!" Well, this time you poke it.
2. Spray painting? go light, if you want to build up paint, spray lightly, let it dry, spray again, let it dry..... (with my cardboard address, I intended to hold it off the wall spray black as a shadow, then later shift the stencil, tape it flat, hit it with a color so that the numbers would look like a drop shadow. But I was happy with just black)

A more direct way to make a very tight stencil would be to lay down overlapping strips of blue masking tape, on something like glass. Lay down your pattern printed on paper. Cut through both. Use the blue tape as your stencil.
A good blue masking tape edge carefully pressed (what's the term for this? rubbed in?) can handle a wetter and heavier paint. One artist I know could lay a 1/4 inch thick layer of acrylic paint, pull up the tape and get a clean edge.

If you want to do something like make an ID for your kayak, your name, kayak name, dates, etc... a stencil is too much work. Look into making decals.

Will