Heroes can only use dark or white magic scrolls allowed by their corresponding magic skill level.
You need 1 scroll to cast magic. The scroll will disappear after use. The effectiveness and duration of the spell depends on the level of the casting hero, number of mages under his command and the level of the mage staff artifact. 1 AP and a certain amount of mana is used for one magic cast.
You need a Mage tower in your settlement to recruit mages.
You need recipes to produces scrolls. To start manufacturing them, copy the recipe into the slot of the Mage tower.
[More about scrolls]