To tie a quill body, you need a quill, which is basically the center stem of a feather, here, one from a dry fly hackle cape. I like the largest ones, which are easily selected from the hide side. Get hold of the feather by its tip, and pinch the fibers on one side of the stem, then pull down. This will strip them free. Continue stripping off fibers until you’re left with a bare stem, other than the feather’s very tip.
It’s imperative that you soak the quill in water prior to tie-in for at least ten minutes, to make it more supple and far less prone to breaking. After the soak, remove the quill from the water bath and blot off any excess water with a paper towel. Then snip the tip off.
Lay the snipped-off tip on the near side of the hook and take thread wraps to secure it. Continue taking thread wraps rearward to the base of the tail, then forward to where you want the body to end. Get hold of the quill and start making touching wraps with it up the hook shank to form the body of the fly. When you reach your tying thread, use it to anchor the quill, then snip the excess off close.