I think a “terminal application” in this case would usually refer to a command line tool which is a throw-back to the days when you had to access larger computers via a “terminal” (rather than having a “personal computer”). You can move files and do all sort of things from a terminal, but it’s executed from a command line.
Your FTP/SFTP application Cyberduck allows you to copy/delete/move files, etc. using a GUI, but it’s actually just doing all these same things as a terminal but with a prettier interface (and without having to know all the commands to execute)
Now… to do the file management you’re looking for, you could use SAMBA to mount the drive of the norns like you would an network hard drive. However, this would still be over WiFi rather than via USB. Installing SAMBA would require a bit of installing extra software on the norns, which may be a bit above your current power-level by the sound of things.
Cyberduck gives you the GUI aspects that you’re looking for here. I’d suggest trying to get the hang of using that first and see how that goes.
Not sure why you’re more keen on using USB to connect rather than WiFi.
EDIT: Also - think of the Norns device itself as a computer - rather than something like a hard drive or MIDI instrument that connects to a computer. Thus you’re networking two computers together.