I just taught myself and learnt off of people I knew, asked questions when I didnt know the answer, eventually got to the stage where I could actually understand the Haynes manual, and in particular, I only concentrated on one car, the Clio 16v. When I look at other engines I still sometimes take a bit of time figuring out which bit is which! but the valver engine bay I know back to front now. Dont be embarassed to ask mechanics for an explanation if you take the car into a garage for work, anything you need to know can be answered on these forums as well.
I still wouldnt say Im any sort of mechanic, I can do most jobs on my valver and then to my joy found out that I am now able to work on my Fiat as well, but it just takes a lot of practice, taking stuff apart and putting it together again, understanding what an engine needs to work etc.
Just the other day I was thinking to myself, I wonder why when you press the accelerator it actually makes the revs increase, how can just opening the throttle do that? I figured it out after a couple of minutes thinking, but it was quite a revelation!