Well for starters, the courier and the multiboard are two very different things there sir. But the basics are, the courier is a unit, which you'll have to give the ability to find the hero, to combine items, and to return to the base, so that requires fiddling with both Object editor and Trigger editor. The multiboard meanwhile requires some fiddling as well with the Trigger editor.
If it sounds a bit too confusing at first, then it could be suggestible that you try to play with the triggers for the multiboard yourself, as learning first hand will always make you learn more than you can ever do if say, given a step-by-step. A good place to start would be to open the trigger editor, and use the category of actions labeled as "Multiboard".
