From where does variable_get() get the first parameter? function variable_get($name, $default = NULL) {
  global $conf;

  return isset($conf[$name]) ? $conf[$name] : $default;
}


From where does variable_get() get the first parameter?
I think you're referring to the $conf variable? 

It's set in sites/default/settings.php (or sites/SITENAME/settings.php if you have a multi-site installation), and that file is included in Drupal's page build.