I have faith in you Mugen!
Okey, let's go
Katon or fire release allows the user to create fire by increasing the temperature of their chakra. Katon is usually mid-to-long-ranged that cause burning and explosive damage. Fire element is strong against wind and weak against water. You can powerup your fire with wind because air naturally feeds the fire.
A sufficiently powerful fire jutsu can be strong enough to overwhelm its natural weakness of water.
Fire jutsu can also be used to produce both lava release with earth and boil release with water.
Common users are Uchiha clan, Kyuubi, Kakashi, and Hiruzen Sarutobi.