Im not really sure what Garbage Matte and Track Matte are so il explain what I did

The way its setup right now is with the other clip on track 2 of the timeline, then I clicked on the transparency settings button and it brings up a screen with all the different types (Im using Green Screen if that matters) and in the preview box it has corner squares that can be moved around to crop the layer into some kind of shape.
I used this to produce a vertical 'strip' so only that section was shown on top of the other video layer. The problem is though there dosnt seem to be a way to control the cut, only the transparency opaqueness (if thats even a word). What I was trying to do was move the strip about but not the video layer underneath.
The closest I have got so far is to do all the above but make seperate clips (copies) and give each a different transparency cut setting for each one, it sorta works but wasnt what i was originally intending. It does somehow lineup with the other tune bit of the music though
I can do a screenshot or something if im still not making any sense ^_^'