Ok, so you have went past the first 2 actions so I assume you know what triggers are and why we use them

Or not ?
Every trigger has Event - Condition - Actions (Conditions & Event are optional, but lets not go there now)
Pure GUI triggers use something called "Variables", very important, every coder loves them. They are very useful as you can set them to whatever you want/need (A few exceptions...).
When you open the trigger editor, somewhere at the top should be a yellow "X" icon, this is the variable editor, this is how you make global variables.
Set TempPoint = Target point of ability being cast
TempPoint is a point variable which you have to create.
To create the action Right click in actions and create a new action.
From the drop-down menu chose "Set Variable" and set the values accordingly. First you chose the left side of the "=" sign so the editor know what variable you are setting as they can take different values and afterwards you set the right side.
Umm... everything ok so far ? Or I miss-understood the problem ?