It depends on the type of database that your are using. If your are using Access DB, then just type the URL for the application in browser' address bar. i.e. http://www.domain_name.com/forum/ For MS SQL Server DB is little more involved. Maybe you want to read the readme.txt that came with the download.
I had a weird problem getting the forum to start working on my server, don't know why it was doing it to me though.
I was running access2000 on the server, and first had to convert my forum db over to access2000 format, then when i uploaded it and went to the site the default page pulled up but was missing like almost every field and i couldn't log in. So i went to the setup.asp page, it said everything was fine and then i clicked on the go to forum link and everything all of a sudden pulled up correctly like it was supposed to. I don't know why it was acting that way, but there's something you could try doing if you're running access