You aim at something, and then adjust until when you are viewing the scope you are actually hitting what you are aiming at. For example..
Aim at an object 25m away, your first shot hits under the object so you then adjust your scope downwards to compensate. Aim at the same object from the same distance, if you hit it then you've zero'd the scope into where you're shooting.
Thanks, I went today and just used it for aiming in general directions, it was quite well zeroed in anyway, it was just in line with the front iron sight