Main Class - sub classes

I've just started AS3. I like to use proper programming methods when I program -开发者_运维知识库 and I'm not sure how to write code in the symbol classes that is recognized by the main document class. If I put all my code into the document class it works fine - but WHAT a mess!!! Surely this can't be how it's supposed to be done?

I've been away from any programming for 3 years, and now am struggling to 'catch up'. Can someone offer the simplest example of main document class calling/accessing information in a symbol class? It would be really appreciated! If I initiate a variable in the main class I know it goes over to the symbol class and checks that public class and public function, but if I put ANYTHING in there (ie: even the variable xy coordinates) my program craps out.

Thank you in advance for any help with this - it seems so basic, it's embarrassing.

Adobe has tips for creating a basic AS3 application here:

Adobe, creating basic application

Colin Moock's book, Essential ActionScript Chapter 29 has a good explanation on how to program the symbol instances.