Fusible like heat n bond light hold your pieces in place so you can stitch them down - they wash away in the laundry. There are some heavy, very stiff fusible products that are permenant- they are heavy, stiff and No- sew.
Glue washes away too, just holds so you can stitch. I prefer heat n bond lite- for me Elmer’s is very difficult to stitch through. I do tons of appliqué and have tried many different products - the heat n bond lite is by far my favorite product.