Right i'm building a forum for a friend and i need to know how to do it correctly.

I've got (forum) for main.
Then i've got (forum_cats) for cat's.
Then i've got (forum_threads) for thread's.
Then i've got (forum_thread_posts) for comment's to threads.
In my SQL tables & so on.

I just need to figure out how to extract them all correctly well the thread_posts one is easy on thread's but i'm struggling with the main forum.php page, i can get it to list (forum) name's & so on and (forum_cats) correctly, i just need to figure out if i do thread's latest thread's meaning how i do it to get it to show on the (forum_cats) bit.

Struggling thanks.