if its your first forum or 'big' application, just build somthing small (a very very simple forum, doesnt have to have templates and stuff) just start off basic then build on it.
I think writing a full tutorial on how to create a forum would be a mammoth task, alot of people dont have the time :(.
Just remember : KISS (Keep It Simple Stupid), you cant expect to jump right in and code somthing with as much features as PHPBB etc, it just isnt possible.

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mysql> SELECT * FROM `users` WHERE `users`.`clue` > 0;
Empty set (0.00 sec)