cPanel is a web-based control panel for site management. It provides CalDAV and CardDAV integration.
User name/password: use the username and password of the email account (= not the cPanel account)
For more information, see cPanel Knowlegde Base: How to Set Up Calendars and Contacts.
Important: cPanel now uses Roundcube as default web backend. In order to be able to see calendars you're synchronizing also in the web view you need to switch to the (older) Horde backend in cPanel.