Stacking = something the trigger does.
Staging = something the shooter does, whether or not the trigger stacks.
As far as staging the trigger, JohnKSa got it. Though you might see a Jerry Miculek vid demonstrating the technique, it's bad technique for 3 reasons:
1. It essentially amounts to timing the shot, which is largely futile.
2. One has to re-start their pull to complete the shot, giving one a 2nd chance to misalign the sights. And when also trying to time the shot, it encourages one to yank the trigger now!! when everything suddenly appears to align.
3. One stages to make an accurate shot. But as ironic and counterintuitive as it may seem, because of the above, staging isn't as accurate as a good proper consistent DA pull.
Staging a trigger can quickly become a habit, and a tough one to break. People typically stage triggers because they haven't mentally committed to the shot before they start the DA pull. Their subconscious knows damned well they're going to stage, so they pull, stage, commit, yank. Make a conscious effort to commit to the shot before starting the DA pull. You can abort if anything from this point on isn't right, but mentally commit to a single smooth pull.
A gun with a smooth consistent action is necessary for a stage-free DA pull, and actions that have a lot of stack pretty much require the shooter to stage, which is why I'd have the action tuned and stack removed, if possible.