Components

Verbal components require the caster able to speak. Somatic spells require the caster able to move. Any spell which is somatic requires hands to be free of weapons or equipment. For every hand that is filled with an item or weapon, the caster is penalized one round. Material components mean the spell requires something to be in the caster's inventory to be cast. Sometimes that material component is used in the casting, sometimes it isn't, it depends on the spell. Spells that are both nonverbal and nonsomatic cannot be interrupted by jars or actions that would otherwise interrupt a spell (getting items, putting items into something else, etc.).