Hi Roaming,
First off, bbpress is not a WordPress plugin.
It’s a standalone forum.
(you’re not the first to think this, as God forbid we’d actually be able to say that anywhere on the actual website)
bbPress has 3 advantages going for it
1) you can share users with WordPress
2) you can share logins with WordPress
3) you can use your theming knowledge from WordPress to make them look alike.
It should be noted that although (now) sharing a very similar looking/acting Admin section, bbPress has it’s own admin section totally outwith WordPress.
As for an installation guide, the good folks at bbPress have cunningly hidden it in their Documentation > INSTALLATION page. I know, who’d have guessed
https://bbpress.org/documentation/installation/
The next bit may sound cheeky, but I just want to be very clear. As bbPress is NOT a wordPress plugin or a wordPress Page or anything like that, it will not in any way shape or form, look like your WordPress blog unless you manually edit the bbPress theme to do so.
I state this really bluntly because:
1) It’s our 3 most complained about assumption – not sure why people complain that their assumptions are wrong but y’know, they do.
2) You’re using Thesis, which 90% of the time means you like menus/WYSIWYG over actual coding. You may ofcourse be in the 10% and be more than happy, which is awesome.
Given how your blog looks, it wouldn’t be hard at all to theme your bbPress forums to look like your WordPress blog
Take care, and good luck!
Kev