Through the various lessons and extracurricular activities you will be allowed to gain new spells and elements. You decide whether or not your character can learn more than one element, but the more elements a character has the less they can "master" an element. In other words a character that dedicates their magic to one element will be stronger in that element than a person who knows two, and the person who knows two elements will be stronger at their elements than a person who knows three, so on and so on. That isn't to say that a person who knows more elements is weaker, since the more elements a person knows the better rounded they will be against other characters. Additionally, a character that knows a certain combination of elements (there are multiple) can learn special mutations of their magic that are stronger than basic elemental magic.