Hi Giovannino
Welcome to Gaia. In my opinion, Gaia is a rather simple framework to get a hold on as long as you:
1. already have some AS experience
2. stick to the Gaia way of doing things (kind of long to explain here, but you'll see)
3. your first Gaia projects are kind of simple, basically navigation, and little to none inter-page communication.
4. keep your complex stuff isolated from Gaia (code it inside one page, or even better, code it in a separate swf file and load it as an asset).
You can do anything over this framework, as it's just AS, but I'll name you a few common pitfalls:
. If you need properties or methods from page A to be called from page B, do Gaia.api.getPage('index/pageA').content.yourMethod(), but don't use strong typing or you'll run into application domain problems (if in AS3).
. Put you initialization code inside transitionIn, not inside the constructor.
. don't code inside Main.as, code inside your pages classes. If you need a "global" place for startup things and that, use the IndexPage, as it's never unloaded.
Check this video tutorials first:
http://totallynerdy.com/, I've found them very useful to beginners.
And you're welcome to come back to the forums for specific questions; just look for them first to check if they're already answered around here

Cheers!