Characters with the ability to cast spells may cast them as spells or as rituals. A spell is cast quickly for rapid results, but the caster is more limited in the spells he can cast. A spell cast as a ritual allows a spellcaster to cast spells above his normal limits (and to an often greater effect) at the expense of more time. Some spellcasters may only cast spells as rituals.
Preparing Spells and Rituals in advance
The Effects of Mana
Known, Familiar, and Unknown Spells
Misc Spellcasting Rules