I allways use a skill saw with a fresh carbibe blade.If you have to ask you probably shouldn't be doing it.but if you must:lay the counter upside down on 2x4s,or some other solid work surface that you won't mind cutting in to.Mark your line with a framing square.then make a line a half inch away and cut that line first.It will give you some practice and take weight away from your real cut.If you are not very acurate with a skillsaw cut a little proud of your line and then belt sand the rest.Same saw for a sink hole but finish the corners with a sabersaw