We have several shooting fundamentals: grip, stance, sight alignment, sight picture, trigger control, breathing, follow through and recovery. In this video we start with an introduction to trigger control adn namely "prepping (or staging) the trigger".
Trigger prep is defined as taking up the slack of a trigger. This process is similar to taking a picture with a modern digital camera. When we take a digital snap shot we first press the button half way to focus the shot then we increase the pressure and "break" a shot to snap the picture. Same principle for shooting a gun. Normal triggers have about 3 lbs of force to take up the slack in the trigger, then the trigger stops, and then another few pounds of force is required to break the shot.
Using the red trigger take up laser you can see whether you are prepping the trigger prior to breakign the shot. When you see the red and green lasers come on simultaneously you are not prepping the trigger.