If you take apart the gun, you will realize what each one does.
The screw with the trigger pull (closest to the bolt side), when you screw it in, the trigger pull decreases.
The screw next to it is the magnet adjustment. This controls how strong the trigger pull is.
The screw in the trigger controls how far the trigger will travel after the shot is fired. This one was a little hard for me to understand. The trigger click is when the ball is shot, and that screw lets you control whether or not you want the the trigger travel to stop there, or for the trigger to keep going back after the shot is fired.
Hope I helped.