http://mponpsecu5qaqu4s7chzbldsp6hu45pwecvr72m26xbf6lo3slqo6tad.onion/docs/INSTALL.html
Point your web browser to the location where you uploaded the phpBB files with the addition of install/app.php or simply install/ , e.g. http://www.example.com/phpBB3/install/app.php , http://www.example.com/forum/install/ . Click the INSTALL tab, follow the steps and fill out all the requested information.