How to build PDO MYSQL database connectivity using PHP

<?php
class Database{
    private static $dbName = 'demo' ;
    private static $dbHost = 'localhost' ;
    private static $dbUsername = 'demo';
    private static $dbUserPassword = 'demo_password';
    private static $con = null;

    public static function connect() {
        // One connection through whole application
        if( null == self::$con ){
            try{
                self::$con = new PDO( "mysql:host=".self::$dbHost.";"."dbname=".self::$dbName, self::$dbUsername,
                self::$dbUserPassword);
                //self::$con = setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
                //echo"Database connect succesfully";
            }
            catch(PDOException $e){
                die($e->getMessage());
            }
        }
        return self::$con;
    }

    public static function disconnect(){
        self::$con = null;
    }
}
?>