Have you created a database yet? You have to create it yourself (or have an installer do it as part of installing a script like Joomla) and create users + passwords.
Log onto cPanel, "Databases" section, click on mySQLDatabases. It will show you any databases you have and any database users. The passwords should have been made when you created the user. If the user was created by a script, there should be a configuration file that is part of the installation that has the password.
The host is "localhost" .