Katon is one of the basic elemental nature transformations. It is performed by moulding superheated chakra inside the stomach before releasing it via the lungs and mouth. There are also variants to this in the form of some mediums such as the use of gun powder, explosive tags and chakra flow into a weapon.
Weakness: Water because it cools and smothers them.
Advantage : is strong against wind because the air feeds the flames