Track Motion in the track header.

You can have Lock Aspect Ratio enabled then when you click the corner to drag smaller, you can put one video in the top left corner and the other on the top right corner. There should be info in Help or use Search here as there should be several tutorials to be found.

switch using composting? I suppose. I do all my editing on the timeline, one active cam and a static cam (or two), then split the active event where I want my cut points then delete the unwanted portion. The lower track will then show instead.

To do my rough cut, I play back at 4x speed, when I get to a point when I don't want the active video, press s (split), when I want to use it again, press s. When I get to the end, I go back and delete the unwanted parts. My fine tuning process is to drag the active event edges forward or back to where I want the cuts to actually be apply a fade if desired. Doing an hour video like that goes lickety split. (Pun intended!)