AI question for hero casting custom spells

Erm...
May i know how to create an AI for computer heroes to cast thier custom spells when they attack enemy?

Do i need JASS? or just normal AI editor? or some triggers?

The automatic AI usage of abilities is hard coded. That means they will try to use the spell depending on what the base spell of your custom ability is. Unfortunately that cannot be modified. AI scripts do not help with it either.
But of course you can use triggers to issue direct orders to the heroes. Just set up a trigger that has events and conditions that make it fire when you would like the ability to be used and then issue the order as action.
If the hard coded AI uses the ability in a way you don't like (too often or whatever) you can also catch the order in an event and counter it.

Usually if you base the ability on the right one you won't get any troubles, you can always have some triggers to order the computer units to use the abilities when needed, and yet they will never automatically use any skill based on channel