Materia are little orbs made by crystallizing mako. Mako is the life energy of the planet. With Materia you can use magic or call on spirits. It all depends on what type of Materia you use. Sometimes you can link materia in linked slots in your weapon or armor. When you link Knights of the Round Materia with Hp Absorb Materia you get an attack that kills almost any enemy and some life back.
