Go to the links in my signature. Also:

google.com/linux

...and start asking questions. Or wikipedia. You'll learn more and faster by asking questions and getting answers yourself than by anyone here spoon-feeding them to you.

Download and burn a couple of 'live' Linux distro CDs. With those, you can try out and learn Linux basics risk-free (run directly from the CD, no mods to your computer) or go ahead and insta!l in a dual boot setup. And of course you have a N900 to learn with..