Making dummy spells

Making dummy spells

So I read the post on how to make spells be autocast, make a dummy spell, etc. But.. Can someone run me through that?

Event-
Unit begins casting a spell
Condition-
Spell being cast is equal to XXX
Action- ???

Edit: To make this easier for me to understand.. please try to explain it as if you were trying to give Unholy Aura the effects of Attack Rate.