Vortexes can either be caused by gravitational pull, or by uneven heating and cooling of the earth's surface. Liquid vortexes are generally created by gravity, such as when water spirals down the drain in the bathtub, while gas or atmospheric vortexes like tornadoes are created by the second method.
Vortexes are formed when two substances move rapidly to replace each other along a vertical track. In the case of liquid vortexes, the substances are usually the liquid in question and the surrounding air. In atmospheric vortexes, the substances are generally hot air, which has a tendency to rise, and cold air, which has the tendency to sink.