Blocking: I wash a wool thing (like a sweater I've just knitted) and then lay it out on a towel to dry. While it's on the towel you adjust it so that it has the shape you want. Let it dry in that shape and it will hold that shape pretty well.

Works nicely for evening out those little knitting oopsies (like stitch tension, which I do a fine job of, but sometimes I'll have a loose or tight one here and there) or restoring the "spring" of ribbing on a sweater that's been worn a lot.

But it's not adjustable enough to shrink a sweater down 2 sizes, when I do it it's more for adjusting the shape or hang of something wool.