Ok, here's another newbie question, that I'm sure once answered by one of you masters, would be a good resource. The guy who trained me to fly, although the flight portion was great, he failed to discuss this all too important facet of RC Flying.

1. What's the difference between running rich and running lean?
2. How can I tell?
3. How does the needle valve work?
4. People who help me tune my plane seem to be listening for something, what is it?
5. Does this play any part in determining RPM's?
6. If so, is there a target RPM range I should be looking for?

Thanks in advance, guys. I know, like always, there will be some very insightful advice to follow.