Essentially, the Preview Window has the following functions:
Enlarged display of pictures. For more info click here.
Viewing and listening to audio files. For more info click here.
Displaying individual video images during cutting. For more info click here.
Display of messages and info
To display the Preview Window, click on View Toolbars and Preview.
The same way the Preview Window can be made to disappear.
The Preview window can be detached from the user interface and enlarged and moved as is customary in Windows. See Customizing the program window.