A tornado is formed when warm, moist air and cool, dry air collide. The different airs then start spinning around each other at a rapid speed and forms a tornado.
Tornadoes only form on ground and cannot form in the ocean.
Tornadoes are large spirals of wind connected from the ground to a cloud, that can cause a huge amount of destruction.
Tornadoes can form in such little time as 15 minutes or as long as 1 hour.