I agree with hogflyer. The rudder is a very important (some would say the most important) control surface. Although it is not often taught early in one's RC training you should eventually learn how to use it properly.

The best book I have found on this subject is Stick and Rudder: An Explanation of the Art of Flying by Wolfgang Langewiesche. You can find it for less than $10 here:
[link=http://www.amazon.com/Stick-Rudder-Explanation-Art-Flying/dp/0070362408]Amazon[/link]