Every character built for this game system is born with a selected race, and from the way of living they get three basic attributes, that contribute to "what they truly are".
It is a simple mechanism that allows you to learn that your adversary is a "rogue leader from a noble family", and get some insight on their mode of actions at a glance.
The process of creating a character is explained here.
There are just three "obtainable" attributes for any character, being race, class and background.
Every character also have the unchangeable race attribute, obtained at birth.
Races are usually adventure-specific. Character's race define his physical features, how other characters perceive them, and provides some modifiers to stats.
You can read more on playable races and their bonuses for the default setting here.
Class means what set of unique skills this character did actively learn on their journey.
Usually classes provide two bonus points, one to stat mod and one for skill progression. By being trained in selected classes you also get a proficiency bonus in their according skills. Class does also represent how other characters see you according to their disposition towards different activities.
You can read more on playable classes and their bonuses for the default setting here.
You are free to build your own combination of points appropriate to the usual activities of your character!
For example: you can be proficient in class of "space technician", with a bonus in body and awareness due to your extensive low-gravity training, or a "herder", with a bonus in presence and endurance due to your life being closely connected with herding mammoths on a frozen steppes.
Role means what archetypical position in the group (and by extend - in world's society) your character represents. It also often serves as a basis in combat or social interaction on what should be a priority for this character.
Usually they give a bonus in appropriate skill, add some flavor, and provide advanced behavior module for a boilerplate of a character.
You can read more on playable roles and their bonuses for the default setting here.
You are free to build your own roles, appropriate to your character's usual priority of actions.
Background means where your character comes from, what knowledge and prepossessions they have, and what will be their own opinions on a nature of the events around them.
You can read more on playable backgrounds and their bonuses for the default setting here.