Put it in your root, but in a folder of its own. So, if you have WordPress here
/home/www/example.com/wordpress/
you can put bbPress here:
/home/www/example.com/wordpress/bbpress/
Then, your website/blog is http://www.example.com and your forum is http://www.example.com/bbpress/
You can call your folder whatever you want, it might be forum, forums, bbpress, anything at all.
Psst! You mean to put bbpress here:
/home/www/example.com/bbpress
If you put it under wordpress, your URL will be http://www.example.com/wordpress/bbpress
No, I meant what I said. A lot of sites are just WordPress sites, so example.com/ gets you WordPress and example.com/bbpress/ gets you bbPress.
The point was only to show the relationship between the folders though. With this information, you can probably figure out where it all needs to go.
You put it in the folder that you want your forum index to be, most people usually make a folder called /forums/ or /forum/ unless you want it to be as the root index of the whole website (for example if the main site itself is the forum).
Another alternative is to make a subdomain like forums.domain.com, I prefer this way personally. Then just put the files into the root folder where the subdomain points. Hope this helps.
