[Advice on how to make a forum from scratch]

I don't think i was clear with my self but i want to maker a forum from scratch.... not vb or anything like that....from scratch.

[How to make a forum.]

Can anyone give me some advice on how to make a forum? I don't know where to start or what to look for. I know a lot of PHP and HTML. I just don't know where to start....Can anyone help?