ok first of all you must have advance or with cpanel.
1) access your cPanel
2) on the 5th row you'll see a folder with a yellow smilie on it (name Bulleitin Board)
3) click on it (this will bring you to phpBB)
or
4) same 5th row go to Scripts Library
5) scrool down to use see Community/Forum, Defult Addon, or Fourm
Hope this help you?