One problem with a Trigger...

I want a trigger that do : if one unit comes in 350 range of other unit, issue the 2nd unit to cast a custom ability... and i dont know what event,condition and action i should put.

events - 'unit in range'
conditions - unitype comparison or player comparison
actions - order 'variable' (just set the unit that must cast the ability to a variable in begin of the game) to cast .......

Download the new WE-Unlimited editor...
there you have MUCH events...

like you not have to create a unit and save the map with the placed unit.

You can create the 1st unit whenever you want and save the unit in a variable.

You should only do this then:

Events: A unit comes in *yourrectinteger* of *yourunit*
Conditions : /
Actions:
Oder triggering unit to *yourspell* on *yourunit* unit.

Or what you ever want to do with the in range standing unit.

WEU = bad!
WEU basicly adds some jass script to your map.
The WEU gui calls thoes functions like the standard functions.
It is ass bad as using BJ calls when it comes to lag.

Although WEU has some advantages for beginer triggerers I dont recomend you use it.

WEU isnt bad, yes it once gave my map an error, but just make back ups often and its solved. people that dunno JASS rly need WEU sometimes