How to achieve this menu effect

First of all, whats up everyone. I haven’t been around for awhile, so just wanted to say hello. Trying to get back into flash is harder than I thought it would be. I saw a neat effect for a menu, you can view it at

http://www.podlob.com/flash/dynamenu/dynamenu.swf

Just keep clicking continue.

Basically, it’s just a collapsable menu, except, I don’t know where to being with making one. Any help is appreciated.