There are MANY xterm tutorials out there to be found by googling. For starters, try as search terms xterm and tutorial.

There are not many significant differences between how xterm works on the N900 and how it works elsewhere. It would be great if someone would write a Maemo-specific xterm tutorial, and it would be easy. Just find a general tutorial, try its commands on the N900, and use the commands that work to build the tutorial.