Actually, screen and midnight commander are both programs that you run in a shell console.
If you've used Windows, you might think of the 'shell' as the 'command prompt'. 'root' is equivalent to 'administrator' in Windows; root essentially has unlimited privileges to read, write or execute any file on your computer.
Midnight commander is a filemanager similar to Norton Commander from the DOS days. It's very efficient; I prefer it over the graphical filemanagers like Konqueror or Nautilus. Try running it; it has self-explanatory menu options conveniently displayed. Tip: use the INSert key to select multiple files for copying, moving, deleting, etc.
Screen is also an awesome program. It's a like a windowmanager for your console. I'm using it right now in an ssh session from my laptop to my server; when I start a job on the server, I can detach the screen, and turn off my laptop but the job will continue running on the server. There's a better explanation of screen over at kuro5hin.org