....... my question is how do I attach the crystal to the end of the staff?
If the diameter of the crystal is smaller than the staff, drill a hole in the end of the staff - slightly smaller than the measurement across the stone's edges. It should be a reasonably easy push fit. Secure it with glue; I use medium-viscosity cyanoacrylate (also known as "Krazy Glue") for this kind of work, but epoxy or good old carpenter's white glue, "Titebond, "Weldbond" or similar, will also work just as well, and is cheaper and easier to use (it doesn't stick your fingers together instantly).
If the crystal is of larger diameter than the staff, drill your hole and then make two saw cuts at right angles lengthways along the staff, for perhaps 4-6 inches depending on the relative sizes of staff and crystal, so what you have is essentially a claw setting. Push the crystal into the claw so that the prongs of the claw spread out to hold the crystal, with a drop or two of glue for security, then bind everything together with brass or copper wire, or heavy cotton or linen thread - or even glittery Christmas ribbon.
That's how I'd do it anyway; have a think, and you might come up with an even better way. Good luck, and post some pics of the finished staff!