Yeah, it can be a bit confusing. So far I find it a lot easier to administer than phpbb2.0.x. For phpbb2 I had to write several custom scripts to block spammers and other issues. It appears those features are already present in phpbb3, so that is cool.
You are supposed to be able to get notifications when someone posts to a forum, but so far I have not figured out how.
I also hate their default forum style. I find it cluttered and hard to find features.
Add: I just figured out forum subscriptions. You go to a forum, (ex: this is posted in the "General" Forum). At the very bottom left of the page next to "Board Index" is a checked option, "Subscribe". The check makes it appear you are already registered, but NO, you have to click the "Subscribe" link and the check will turn to a dot. As I said, I hate the default forum style and its layout.