Sewing machine optional
Fuse fabric to WU (according to directions which come with the WU.)
Cut your shape out.
Peel backing and place on shirt.
Iron again (follow directions for iron settings)
Sew along edges. You can straight stitch or zig-zag.
The heavy duty wonder under says no sewing, but in my experience the edges will eventually come up with general wear and washing, so sewing is an extra step that will help it stay.
This is really how my "photo op" went.
Happy Love Day!