Dispel allows to end a lasting spell, curse, or ritual, as well as neutralize (some) magical automatons. It can not be used to end a spell that is being casted at the moment, as well as to remove the effects of the spells or curses, such as changed shape or madness.
Dispel allows you to end a spell/ritual/hex within the range of this spell. This spell can cancel magic with a duration and can be used as a defensive action to block magic attacks with or without physical components. To cancel a magical effect you must spend half as many Stamina points as the caster spent to cast the magic and make a Spell Casting roll that beats their casting roll.