Choose your fabric and shape. I chose to use a heart. I used PostIt Paper, which is really hard to find any more but you can use any scrapbooking paper that has been ran through a sticker maker. You could also make a sheet of sticky paper by overlapping painters or masking tape.
Place the shadow of your shape on the fabric, and get your paint ready. If you do not have a foam brush or stencil brush use a rolled up paper towel! (as seen below)
Pat out the paint on the fabric, make sure to use a lot of paint but not so much that it will run!
Wait at least 10 minutes to remove the stencil, then let it dry completely.