Tornadoes come from Supercell thunderstorms, really big and violent storms, when the updraft has a rotating motion. If the updraft goes down low enough, it will cause a wall cloud to form, and then a funnel cloud will come down out of it and when it touches the ground, boom, a tornado is born. Tornadoes can cause all kinds of damage, although they are mostly short lived. From picking up a house and turning it into kindling wood or picking up a boy, sending him flying for several miles, only to be found later (see the Little House on The Prairie Series. I can’t remember which book). Interestingly, if you are looking at it on a radar, a tornado might show up as a little dot of heavy precipitation, which is the radar picking up derbies. Also, as the tornado comes from an updraft and rain comes from a downdraft, there is usually not rain at the site of a tornado.