The preview area of the main window is where you can view your presentation before exporting it.
You can scrub to a particular time in your presentation by moving the Scrubber in the Timeline.
Pressing the "start/stop" button (), which is just below the preview area, will play the presentation.
The Preview area is also used to edit various aspects of your presentation:
Positioning Clips
You can resize, move, and crop the bounding rectangles of your
clips directly in the preview area.
Crop Canvas
You can crop the overall canvas. This is one way to quickly focus
on only one area of your screen for the duration of your presentation.