LCguy is right -- if it's already broken, then it's hard to make things that much worse.

And that's what you need for your first repair experience -- a junker already destined for the scrap heap. I'm willing to bet that the satisfaction you'll feel from bringing the dead back to life will encourage you to do more. Then you'll eventually get to the point where you'll feel confident about opening up a still-working machine to do upgrades and light maintenance. But first things first: Find a DOA Mac (there are so many!), and revive it.