[Naox]

I would do as Ankita said and save the data in a database, checking to see if their credentials validate. If so, create a session (session_start();) and input their username. Then header("Location: nextpage.php"); to the page you want them to view once they login successfully. on top of the nextpage.php, do a start_session() and if $_SERVER["username"] == "" then redirect them back to the login page. this way no user could get to the nextpage without logging in successfully