is this stuff just regular fusible web? also can i fuse three pieces of web together say if i were making a card?

Yes it is a fusible type product, like wonder under. I am not sure why you would need more than one layer of it though?
One piece will fuse two pieces of fabric together. You would iron the fusible to the back of one piece, peel off the paper and then fuse that fabric to the back of another piece of fabric (or the post card) :D:D:D

In my experience, it doesn't hold well w/o stitching. (Tried it for a hem that lasted one washing!)