Google the term "forum scripts" to get started.
One question ... do you already have a defined market that you know are ready to visit your forum?
If you don't ad you setup a forum "just because" you'll end up feeling quite frustrated with your efforts and think someone is after you!
Just kidding.
It is honestly a lot of work, so groundwork is essential. It also takes some skill, dedication and personality because forums attract all sorts.
Think of it this way, you wouldn't open a shop without knowing people would come.
The internet and all its activities is no different.
Hope this helps
Best of luck.
'Bayo
Yes,
Bayo is right. Your see you should have a vision. Don't just set up a forum bcos others are doing it. Who is your target and what plans do you have to maintain it.
Do you have enough time to spend online?
What do you do with spammers and scammers?
And how do you prevent them?
These and too many other questions are there for you to answer.
I will be telling you more about this later.
Shalom!