A role is like a class, but is more about how you play your character than what it does. There are several roles to choose from at the beginning, and you can unlock more as you progress. A role is different from a class, commonly used in rpgs, because a given role doesn’t give you any abilities, but is actually more of a restriction, a direction, and a perspective.
Click through the list to the right to review different roles. Choosing one isn’t totally necessary, but again, it adds further dimension. And of course, everyone plays a role one way or another, whether they choose to or not.