Fire, is one of the five great elements, it needs three conditions to stay alive, heat, air and something to burn. If you remove one of the things, you will extinquish the fire, but if all of these things are available to the fire, it can become an unstopable force, which will burn everything to ashes. If you don't stop fire it can burn through everything, even stone. Fire sadly, has an enemy in one of the other five great elements, water, which is able to take away, two of the three things needed to maintain fire, burning material, and heat. But if used correctly, fire can turn even its arch enemy water into steam, thereby making it useless against it.
The nation who uses fire the most, is the fire country, especially the Uchiha clan is fond of fire jutsus, and are able to use them with deadly force.
One of the most normal fire jutsus is.
Name: Fire Release: Great Fireball Technique (火遁・豪火球の術, Katon: Gōkakyu no Jutsu;
Type: C-rank, Offensive, Short range (0-5m)
After performing the necessary hand seals, a ninja inhales air via their mouth and, utilizing a large amount of fire chakra, spews a large fireball from their mouth, incinerating everything in range. The fireball ignites externally (as evidenced by Kakashi Hatake's ability to use the jutsu without burning his mask). The Uchiha clan uses the technique as a "coming of age" technique. This technique apparently requires more than average chakra reserves and most Genin should not be able to do this technique.