Zooming requires changing the scale properties of an object, so if you need to zoom in on the whole stage, then you need everything in that stage to be inside an object that you can scale. If you need to zoom into a particular point then you need the registration mark of whatever holds the content to be at the that point of the object. If you need to be able to zoom in on different places, you need to have that object inside another object and zom the outer object.
How do you change and/or find the registration point? So if I set the registration point to where I want to zoom in and then transform that object (let's say I select the whole stage) then that area will move to the center of the stage when you enlarge it?
The registration point is easy to find... it is where x and y = 0 (and z too, but that probably doesn't come into play here). If you tell an object to be at x=20 and y=20, then the 0,0 registration mark of that object gets placed at 20/20 relative to the coordinate system it occupies.
If you scale the object, then it scales relative to its registration point, essentially meaning that the registration point is the only part of the object that does not move as the scaling takes place.
So if your registration point is at the center of the stage then the object will zoom relative to the center of the stage. But if the registration is off to the side somewhere, then it will scale relative to that location instead. You should do this as an experiment for yourself to help you undertsand it... likely much better than anyone trying to explain it.
If the point you want to zoom in on is not centered on the stage, then you probably want to place that object inside another object who's registration point is centered on the stage, and then move the inner object (leaving the container centered) until the point you want to zoom in to is at the center of the stage. Then you scale the containing object, not the object you moved.
So you could have a scenario where when you want to zoom into that point that is off to the side, you start zooming the container (which is centered on the stage) and you also start moving the inner object to have that desired zooming point moving into that center position.
Here is a link to an example file I just made to demonstrate what I am trying to explain.
When you run the file you will see that clicking on A or B zooms into (or out of) that location.
A and B are movieclips within another movieclip (called map). They have clicking code assigned to them. The map movieclip is centered inside another movieclip named mapholder - basically meaning both movieclips have their registrations centered relative to the content they contain. mapholder is centered on the stage.
The map movieclip is moved to bring the desired object (A or B) to the center of the mapholder. The mapholder is zoomed so that the object being centered appears to be getting zoomed in (or out).