What's a trigger to dmg with spell

[Weetbix]

I made a channeling AoE skill but i dont know the trigger to get the spell to do damage. Can someone tell me what this trigger is?

 

[tooltiperror]

> I made a channeling AoE skill but i dont know the trigger to get the skill to do damage. Can someone tell me how to do this trigger​

...What?

I have no idea what you said.

 

[Slapshot136]

• Unit - Cause (Triggering unit) to damage (Picked unit), dealing 500.00 damage of attack type Spells and damage type Normal

something like that, only within a periodic trigger that picks all the units within range of where the ability is being cast?