A Scroll is a magic item. It is a physical storage device for a single spell, which can be used only by a caster. Casters may create a scroll or scrolls on their turn, for a significantly higher cost in juice than simply casting the same spell.
Even a caster who is normally not proficient at casting spells beyond his own discipline can use scrolls of other disciplines with some effectiveness.
It is not clear whether casting a spell from a scroll spends any of the caster's juice.