This fly tying tool serves two purposes: As a bodkin it is ideal for applying head cement to your fly.
To use as a half hitch tool:
(1) Wrap the thread around the end of the tool as if making an overhand knot.
(2) Conceal the eye of the hook in the cupped slot of the tool.
(3) Allow the thread to slide off the tip of the tool over the hook eye thus knotting it on the head of the fly.