A cheaper alternative for grinding and shaping
They're super simple...just dip them in water and run along the glass edge, nice and flat, to take off any flares. If you need to grind to shape, run the stone all along the edge first, so you don't cut yourself, hold the glass firmly and just rub away. It will take a while. You are better off grozing if you have more than about 1/16" to take off, then follow with the stone.