Stencils are useful for creating designs that can be replicated on various surfaces ranging from walls to T-shirts. If you are unable to find a specific stencil design in stores, it's not difficult to make your own stencil for free.
Draw your desired pattern on the cardboard, stiff paper or plastic sheet using a pen. Draw one simple shape for an easy pattern. For more detail, draw a pattern that includes multiple sections; for example, draw a flower with separate petals.
Place the cardboard, stiff paper or plastic sheet on a wooden board set on a flat, stable surface.
Cut out the shape or shapes you drew on the cardboard, stiff paper or plastic using your utility knife. The board you placed underneath will prevent damage to any other surfaces as you cut.
If you only intend to use your stencil once or twice, cardboard or stiff paper will work. A stiff-but-thin sheet of plastic is much more durable and easier to clean, and therefore a better option if you intend to use the stencil several times.