What is the main part of starting a forum??

[mediadrug]

1. Install the plugin
2. Set up some test forums or import a forum
3. Create a WordPress page for your forum display
4. Amend any other settings
5. Hidden vs. public forums – decide which or a mixture suits you
6. Decide on registration/user logins – automatic or manual?
7. Manually adding users to your forum – if you have chosen this route.
8. Make sure bbPress uses the page template we want
9. Add a custom sidebar or use existing sidebar with conditional logic

What exactly are you implying here? OP has asked about starting a forum. Not adding a forum script in wordpress.