so youve set up the database and put the files on the ftp.
go to: yourdomain.com/phpbbfolder/install/install.php
obviously change yourdomain.com and phpbbfolder to whatever youve got
Well maybe he downloaded the latest phpbb from the site, but just upload the .zip file using the Cpanel. Then go to the file via the file manager, and extract the file. It will make a /phpBB3 directory. Then go to www.yourdomain.com/phpBB3/install
follow the steps and you'll install php. The delete the install directory and your good to go