A tornado is a powerful, spinning column of air which touches both the surface of the earth and the clouds above. Tornadoes come in many sizes but usually look like a funnel, whose narrow end touches the earth and the wider end touches the clouds above.
A tornado is so powerful that it can pick things up and throw them through the air. They can cause a lot of damage and destruction to farms, towns and roads. They can easily smash things and kill people.
If a tornado is coming the best place to hide is in the cellar. Although you would need to listen to the strange howling, shrieking and wailing of the wind you would be quite safe there. The best thing to do is to try to stay calm and make yourself comfortable as you wait for the tornado to pass.