The casting of spells, clerical and magical, is a very important aspect of play. Most spells have a verbal component, and so must be uttered. Most spells also have a somatic (movement of the caster’s body, such as gesturing) component. Some spells have a third component, that of material (an item or substance required).
Each character able to cast spells can remember only a certain number at any given level. (This number can be modified by magical means.) Once a spell is cast, that particular spell is wiped from the mind, forgotten, but another spell of the same type can still be remembered, i.e. the spell caster can have several of the some spell memorized and prepared for, within the number limits for his or her particular class and level.