Start with learning the basics of buttons, then get real familiar with the load movie actions, think of them as different levels, and get used to working that way. You can put your whole site into one movie, but the file size will grow quickly.

What I generally do is have a container movie, that loads the different movies into the correct levels. The menu is generally on the very top while the background, is of course on the bottom,if you have an intro movie, you can use it as your container, by having it load the proper pieces into place when it finishes.

Set your buttons up to load your pages into a lower level(generally 1 or 2). If you have pages(loaded movies), that have submenu's, you can load pages off of them into even higher levels(remember you'll have to unload these somehow later), I generally never have a need for more than 5 levels.

A good thing to note, is to have all the buttons on your main menu load everything to the same level, that way you never have to unload anything, because anything loaded onto that level will automatically unload anything that is already there.

Anyway, the best thing to do is dive in and play around till you have a good enough idea of whats going to start building your site. Then come up with a solid plan for your site, and go from there.

Here a site I've been working on for a while now(too long actually, but thats a whole other story), it should give a good idea what can be done, each link loads another movie into the main movie(container),except for anything opening in a new window. Other than the HTML, the whole site was done in 3dfa:

http://www.darksideskates.com

Good luck, and feel free to ask about anything you have trouble with.

-Jason