Like any other class, Loremasters gain proficiency in their spells and skills based on usage. Usage of spells and skills is tracked via Deeds, and each completed deed updates, and gives a buff or other added attribute, to the associated spell or skill.
Deeds can be considered as a more epic version of a normal quest, since you may be asked to do one activity over several hundreds times before you're rewarded with something special. Fortunately not all the Deeds are like that. Some of these activities include killing a specific creature or using a particular skill; it can also be finding all areas or completing a number of the quests in a region. Deeds are worth all the trouble and time spent completing them if you realize the rewards at the end of the trip. The rewards are called Traits, adding special abilities for your character.
The Guardian is the figurehead of any fellowship. They guard the way between their weaker allies and the enemies that challenge them. Their duty is to protect their allies from harm and to take the beatings everyone else should be receiving.
Their ability to wear heavy armour and defensive skills enable the them to face creatures that would make other heroes' morale fail. Most importantly though, Guardians also have the ability to draw foes' attention away from their allies and to themselves.