Spell Completion
This is the activation method for scrolls. A scroll is a spell that is mostly finished. The preparation is done for the caster, so no preparation time is needed beforehand as with normal spellcasting. All that’s left to do is perform the finishing parts of the spellcasting (the final gestures, words, and so on). To use a spell completion item safely, a character must be of high enough level in the right class to cast the spell already. If he can’t already cast the spell, there’s a chance he’ll make a mistake. Activating a spell completion item is a standard action and provokes attacks of opportunity exactly as casting a spell does.
Spell Trigger
Spell trigger activation is similar to spell completion, but it’s even simpler. No gestures or spell finishing is needed, just a special knowledge of spellcasting that an appropriate character would know, and a single word that must be spoken. Anyone with a spell on his or her spell list knows how to use a spell trigger item that stores that spell. (This is the case even for a character who can’t actually cast spells, such as a 3rd-level paladin.) The user must still determine what spell is stored in the item before she can activate it. Activating a spell trigger item is a standard action and does not provoke attacks of opportunity.
Through 3rd level, a ranger has no caster level. At 4th level and higher, his caster level is one-half his ranger level.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.