Alright. So I wanted to create this zealot with this ability.

1. It can select a unit 30 units away.

2. It charges at that unit with 80% acceleration in movement speed. (I'm assuming this is going to have to be a buff tacked on his some behavior)

3. Upon arriving it does 1800 damage followed by some cool High Templar psionic storm affects on the immediate area.

I can't really figure out exactly how to accomplish this. Is it an ability? Or will I need to create triggers to accommodate this.

Psi storm is an effect. You can add "High Templar - Psi Storm (Persistent)" as an effect for your ability, and it will add it. You may have to create your own effect/ability if this does not yield the result you want.

A trigger would just be checking if the ability is being cast and then placing an actor model at the position of the unit being attacked. You would probably want to manually kill the model yourself after waiting for a desired length of time.

1. You can set the range to 30.
2. This is a behavior. Your ability would trigger an "Apply Behavior" effect. The Behavior would increase movement speed on the Zealot. Here's an example of a custom Zealot "Charge" ability: http://www.galaxywiki.net/index.php?title=Designing_an_ability
3. Like Roy said, you would have the final affect be the Psi Storm, though make sure you change the amount of damage it does (keeping it mind that it does periodic damage, rather than all at once).