Until you have learned about Natural’s family of windowing commands, and their capabilities, individual commands will be quite meaningless.
Just in case you are really curious;
L25C20 sets the size of a window
B3/45 positions the window on the screen
F frames the window
If you have access to Natural documentation, you should look up “terminal commands”. You will discover that % followed by almost any letter of the alphabet does something in Natural. There are screen scraper commands, recording commands, windowing commands, etc.