Element rules

There are five main elements in the Naruto universe. Those are Fire (Katon), Wind (Fuuton), Lightning (Raiton), Earth (Doton) and Water (Suiton). Each of these elements are used in different Jutsu and usually have different effects when elemental chakra is channeled through weapons. As a C-rank or lower ninja you can have one element, but as a B-rank or higher you can have two.

Some Kekkei Genkai (clan abilities) also allow combining elements to create new ones. For example:
Water + Earth = Wood (Mokuton)
Wind + Water = Ice (Hyouton)
Earth + Fire = Lava (Yoton)

Different elements are also powerful against each other, like Rock-Paper-Scissors. Fire beats Wind, Wind beats Lightning, Lightning beats Earth, Earth beats Water and Water beats Fire. Get it?