It's a way of creating an isolated filesystem within another filesystem. The chroot'd filesystem cannot see it's parent filesystem and any processes running in that chroot'd environment cannot access or influence the parent filesystem.
As a newbie i recommend getting familiar with the existing linux distro on the box before moving up to the full Debian distro.
What would be cool is if someone could find a way of booting N2100 off a front USB mounted disk if found (or if e.g. a certain file found there) otherwise boot the "normal" system. That way the new system could be loaded on a flash memory drive and if there were any problmes the N2100 could just be rebooted with the drive taken off the USB - clean and easy (and safe!)
Thank you so much for your answer. Your right of course, about the learning stuff. I just bought a book on getting started. I'll finish that one first.... I just never thought that Linux would be this much fun