Place the image you want to turn into a stencil on a flat work surface with the right side facing up.
Top the image with a sheet of glass.
Place the Mylar sheet on top of the glass and tape the edges in place.
Turn on the wood burner and wait for it to get hot. Some brands have a light indicating when it is ready to use, while others do not.
Trace around the edges of the design with the wood burner. You should be able to see the design through the glass. Slowly trace the entire design, and then lift away the cut-out portion. The remaining piece of Mylar is your stencil.
Use the tip pf the wood burner to refine any jagged edges, and then remove the tape from the stencil and use as desired.