Primary skill
Primary skills are qualities of heroes but also qualties of creature. There are four different primary skills: attack, Primary skill_skill#defense, power and knowledge skill. Attack and defense can be categorized as might skills while power and knowledge are magic skills.
Attack skill
Attack skill together with defense is the one of the main factors affecting the amount of damage creatures under hero's command deals.
Spells altering attack skill
Defense skill
Defense skill together with attack is the one of the main factors affecting the amount of damage creatures under hero's command deals.
It should be noted, that while defence is acceptable spelling, it is always spelled defense in Heroes of Might and Magic III. However, it is spelled as defence in Heroes Chronicles.
Spells altering defense
Spell power skill
Spell power (also just power) is the main factor for damage and duration of the spells. By default, all heroes start with at least one point in this skill. However, a mapmaker might set the starting skill to 0. In that case, the hero will look and function as if he had 1 point, but when he receives his first point, it will not have any effect.
Knowledge skill
See also
There are four primary skills:
Attack, boosting your creatures' damage.
Defense, boosting your creatures' defense against normal (non-magical) attacks.
Spell Power, boosting the effect and/or duration of your spells.
Knowledge, boosting your Spell Points, which are used to cast spells.