Stats are a measure of your character's various abilities.
Primary stats are stats that are influenced directly and only by leveling. The three Primary stats are Power, Stamina, and Wisdom.
Power influences damage done by physical attacks. It, combined with Attack, determines damage dealt to enemies.
Stamina is a measure of your character's survivability. Stamina adds HP and combines with Defense to determine damage reduction. Stamina also plays a role in secondary effects of certain skills .
Wisdom affects damage and reduction of spells. It is combined with the Magic Defense stat to reduce damage from spells and projectiles, and combined with Magic Attack to determine spell damage.
Secondary stats are stats manipulated only by your equipment. These can easily change on player preferences and cannot be changed by leveling.
Attack is combined with Power to determine damage.
Defense is combined with Stamina to determine touch damage reduction.
Magic Attack is multiplied with Wisdom to determine Magical spell damage.