Actions:
Units, Leaders and Extras each perform different purposes and tasks within your Usurpation. Some actions can only be accomplished by a collective (Units) and some can only be accomplished by those with the authority to act on behalf of the Usurpation (Leaders). Extras, typically, can only augment or assist others in an action (or teach skills/spells.)
Units can:Leaders (Both Chief and Cohort) can:
Extras can:
* You can only Interrogate once you have a Prison.
† You can only Craft Items once you have a Workshop.
Extras cannot perform actions of their own. They may only join Units/Leaders on their actions or perform actions unique to themselves.
The bonus that they provides indicates the manner in which they are allowed to accompany other Units/Leaders. If they provide a scouting bonus - they may accompany a Unit that is scouting. If they provide a combat bonus - they may accompany a Unit on a raid or attack.
The ability/spell that an Extra may have also lets you know what they may do other than accompanying Units. Typically an Extra can either ACCOMPANY or perform its special action/ability. (Extras that have combat-affecting spells may use them in combat when they accompany.) Any Extra that can teach a spell/skill - also HAS that spell/skill.
-- Note: Extras that provided bonuses while in the lair (such as Architects and Crafters) can provide their bonuses to multiple actions, so long as they all take place in the same Lair. This is generally true of Leaders as well.
Example: You assign 1 Unit to Renovate your Throne Room, and you assign 1 Unit to Construct a new Living Quarters. If you have an architect-type Extra (who gives bonuses to Renovation and Construction), that Extra will provide their bonus to BOTH actions.
Note: All Leaders (regardless of race) have an overland speed of 3. They do not have a Combat Speed.