You need to create your database first and then install your BB script. Use the DH Control Panel to set up your database (names will become clear when you make your database). Enter that information into your config file (either manually or during the install process, depending on the script).
vb is a good forum but if you are completely stumped, DH has a one-click install of phpBB. In your DH control panel, look for Goodies, One-click installs.
To change the directory you will use htaccess to make a Redirect. It’s easy, look at the DH Wiki or search this forum for info.