stitch witchery, wonder under, steam a seam and heat and bond are all fusable webs.
the first one has no paper on one side, it is simply the fusable. the others all have a paper side, so you can draw on the paper, fuse the non-paper side to the back of your fabric, let cool, cut out your design on the lines you drew, peel the paper off and then iron that side to your background
some are stiffer than others, some are hard to sew through, some are easy and soft. it all depends on your project (and personal choice) which you should use at any given time.