Spell Mana is used to cast spells with a Spellbook. The maximum amount of mana, and the speed at which it regenerates, may be increased by wearing special Mage Armor or by applying the Mana Boost or Mana Regen enchantments on your gear. Additionally, you will gain bonus mana and regeneration for each glyph unlocked in your spellbook.
Adding glyphs to your spell book will also increase your maximum amount of mana and mana regeneration. This bonus also scales with the tier of your spell book.