No fusible web is what you use when you want to stick two pieces of fabric together,like in applique,and some craft items.Interfacing is what you use in collars,cuffs,and the lapels on shirts etc to give them body and stability.
HTH
Kathi

Fusible web is just the fusible stuff without being attached to any paper. Sort of looks like a goofy spider web with no design and bit stiffer.

There is another fusible I use, for applique, that's on paper - it's easier for me. The rough side is the fusible. I draw on the paper side, cut it out a bit bigger, iron it down and trim to the lines. Peel off the paper and iron to the the background fabric.