And the explanation…

class Singleton {
    private static $instance;               // static variable to hold our 1 instance

    public static function getInstance() {  // function to get the 1 instance
        if(!isset(self::$instance)) {       // this will only run once (and instantiate once)
            $c = __CLASS__;                 // get the class (Singleton)
            self::$instance = new $c();     // instantiate the class and store it in our variable
        }
        return self::$instance;             // return the instance
    }

    public static function myFunction() {   // we can get to this through Singleton::getInstance()->myFunction()
        // ...
    }
}