To install phpbb on your localhost, you must setup apache and mysql first. We have already posted a tutorial on How to install and configure Apache,PHP,MySql and phpMyadmin on ubuntu. Please read first.
Go to phpbb website and download the latest phpbb stable Full Package in tar.bz2 format or .zip format on your desktop and extract it. Now you will get phpBB3 folder.Just rename that folder to phpbb.
2.Copy phpbb to /var/www folder