The listener object is usually the player sprite. You place the positioned audio on the object where you want the sound to come from. For example, if you have an explosion, you can place the sound to the explosion. Then the closer the listener object (player) is to the explosion, the louder it will be. Of course it's not just the volume, if the explosion is to the right of the player, it will be heard in the right speaker etc.
Edit: By the way, there's an example capx that comes with construct 2 in the example files. If you haven't already, you might want to take a look at it.