mechanics is seriously a "learn by doing" process. you can read books, but until you're actually getting the grease and oil on your hands, you won't truely understand.
however as a supplement, forums like these are excellent. look in things like the performance and maintenance sections to pick up little tips, and gradually as you start to tinker with the car, you'll realise the what and why of cars and car mechanics.
if you look at the "HELP, MY CAR WON'T START!@!!!" (or something similar) threads, thats usually a pretty good start, as a process of reverse engineering. by dsicovering why something isn't working and then fixing it, you conversely discover how it works.