Measure the width and length of your desk surface.
Visit your local home-supply or hardware store and ask an attendant to cut a piece of plywood in your desk's exact measurements.
Place the plywood on a wide, flat surface covered with a drop cloth.
Apply the stencils of your choice to the plywood. Secure the stencils in place with painter's tape.
Squeeze acrylic paints on paper plates. Dip sponge brushes into the paint and carefully paint over the stencils. Allow the paint to dry.
Apply a coat of polyurethane across the surface of the painted plywood. Allow the coat to dry completely before placing it on your desk.