The N900 file system deviates a small bit from your more standard Linux distribution, though I guess all Unix like operating systems deviate from one another in a few significant ways.

Like JadeH said, the best way is just to go looking and see what you find - keep a search engine handy and don't forget to look up man pages for any and every executable you come across.

apt-get install man-browser

It's a long and steep learning curve, but definitely worth the effort.