Some important global configuration settings are stored in configuration.php located inside Joomla! root folder.

This is an excerpt of a hypothetical configuration.php file

<?php
class JConfig {
  ...
  var $host = 'localhost';
  var $user = 'my_user';
  var $db = 'my_db';
  ...
  var $sitename = 'My Great Joomla! Site';
  ...
}
?>

If you need to know the value of one or more of these settings you can use the getCfg() method of JApplication.

Example

$app =& JFactory::getApplication();

echo $app->getCfg('sitename'); //outputs site name
echo $app->getCfg('host'); //outputs database host
echo $app->getCfg('user'); //outputs database user
echo $app->getCfg('db'); //outputs database name

The example should be clear. We get a reference of the global JApplication object, then call getCfg() passing an identifier of a member variable of the class JConfig as argument. The function returns the value of that particular setting.