Capri set has the trim on it to show what the how to is all about.
Top, middle and bottom shows drawing on transfer paper, paper ironed on the back, peel paper off and iron on the lining.

B: tiny zig zag in matching color on the very edge of the wings, cover body in a darker thread coverint it solid. Use fray check or Fray block around the edges, let dry well.
Second picture shows cutting away the extra fabric.

Bottom pictures shows completed butterfly.

Attach butterfly by stitching around the edges of the body only.  Either embroider black "feelers", thin scripto perm. marker or heavy carpet thread with a knot on each end and tack in place.
Bend the "wings" up and curve. The same idea is good for some flowers, etc.