New to PunBB Development

Hi guys, I'm looking to use PunBB as the basis for a site I'm developing for a client. They're after a basic portal with some extra features thrown in (i.e. a directory service - listing businesses that provide specific services, split into different categories).

Now I can do all of what they want, I just need a bit of a head start with regards to the PunBB side of things - i.e. I'm planning on using the scripts own user authentication system to block access to specific pages based on user group, as well as use PunBBs templates and such for the headers, etc..

Can someone point me in the right direction for the quick-start guide on how the user authentication works, and what code I'd need (the basic template, if you like) that I'll need to work from.

I'm sure all of this information must be readily available, and I have looked for it, but I guess I'm not very good at finding it. So if someone could help me out, it would be grand.

Thank you