If you install plogger as a subdirectory of your website, it automatically installs an index.php file in that subdirectory. That means when you select a URL or domain address in your browser that identifies that name it will try to run that index.php file. When it does it will run plogger (plogger.php).
The URl might look something like http://mywebsite/plogger or http://mywebsite/PloggerDirectory depending what the configuration you used in the installation.
When you run plogger it will ask for your installation login.