A role determines the set of options, abilities, and statistics a PC has within a given scenario. There are three types of roles, one for each type of scenario:
Roles provide the base Hit Points (HP), Endurance Points (EP), or Will Points (WP) for combat, exploration, and interaction respectively. These values define how much damage the PC can take before they are defeated. HP, EP, and WP normally cannot fall below 0.
Additionally, Class and Profession roles have an entry for Initiative, and each role has a special dice entry unique to each scenario.
Each role also contains an ability, the name and description of which are provided in detail. Every role has its own unique ability.
Deckbuilding uses roles in a central manner. While there exist generic cards that any roles can include, many cards can only be used by specific roles. These cards will make up the majority of almost any deck and define the mechanical behavior and capabilities of the character within scenarios.
For more information, see Player's Guide Chapter 2: Roles and Levels.