You place the wonder under and the cut out applique design right sides together ( fusible side of wonder under to right side of fabric) and stitch around the outside edge. Then you cut a small slit in the wonder under and turn the applique right side out. this way you do not have any raw edges. You fuse the wonder under to your main fabric or block with an iron and it holds your applique in place while you either hand stitich or machine stitch around the outside edge of the applique.