Violent columns of wind raging at speeds of 100 mph are classified as tornadoes.They are formed just before a thunderstorm when a layer of moist air lifts that of a dry layer. This forms a tunnel that lifts and takes moving over large distances.
There are different types of tornadoes - supercell, landspout, gustnado, waterspout, dustdevil and firewhirls. One can predict a tornado by watching for dark skies accompanied by loud whistling sounds.
When encountered by a tornado it is best to head towards the highway, away from its direction. If it strikes when you are indoors, then the best place would be the basement or any windowless room. And if you are inside a car then the best thing to do is to get out of the car and take shelter in a building.