Spray the back of the stencil with a coat of spray adhesive and wait 15 to 20 seconds for the adhesive to become tacky.
Adhere the stencil to your wall or windowsill in the area you want the stencil to appear. Use a level at the top of the stencil to make sure it's straight. Smooth out any bubbles or wrinkles in the stencil with your hand, and rub along the stencil cutouts to create a good bond between the surface and the stencil.
Pour the acrylic paint color of your choice onto a paper plate. If you are using several different colors on the stencil, pour each color of paint onto the plate.
Dab a stencil brush or sponge into the first paint color and swirl the loaded brush or sponge onto a paper towel to remove excess paint. There are two basic methods of stenciling -- stippling and swirling. Stippling produces an even coat of paint with little depth and shading variation. Swirling produces depth and shading as you vary the pressure on the brush or sponge. To stipple, dab the open areas of the stencil with the tip of the brush until the entire space is colored in. Swirling involves flattening the brush tip slightly and using a circular motion to fill in the open spaces.
Add shading to the stencil by painting just along the edge of the stencil using the stippling method.
Allow the stenciled paint to dry before removing the stencil.