Basically, i want to do this:
ObjectX = For the example let’s say a cube
Y-external program = A steam game
When objectX is used/interacted with, launch Y-external program.
That is as simple as i can describe it. I Hope someone out there can help us with a direct solution or some waypointers for what we are looking for/should be looking into! 
Which bit are you having trouble with? Is the player meant to click on ObjectX to interact with it? If so, you need to look into OnMouseDown() or using a Raycast.
Or if you want the character to interact with ObjectX by touching it then you should add a collider set to be a trigger and add a script that listens for tbe OnTriggerEnter() callback. Or something else? (“Use/Interact” is a pretty vague word and you’ve not told us any more about the style of game).