Might is a measure of a character's muscle power, fitness, and fortitude. It modifies combat rolls with impact weapons such as axes, clubs, and pole arms, feats of strength such as opening stuck doors, and the amount of weight a character can carry. It also adjusts rolls for hit points to a lesser degree.
Wit represents the faculties of the character's mind, including memory, intuition, will power, reason, and understanding. It modifies the number of spells a spell-caster can memorize at once, the maximum number of languages a character may learn, and saving throws vs magic.
Agility is the character's coordination, quickness, and ease of movement. It modifies combat rolls with precise weapons such as daggers, swords, and bows, and the character's Armor Class.
Presence is a character's personal bearing, charm, and magnetism. It affects the reactions of monsters and NPCs, the maximum number of retainers and henchmen a character may employ, and their morale. For spell-casters, it also negatively modifies a target's saving throws vs. spells.