Do you want to redirect the user to any other page, when some task is performed.

It is simple and you can do it easily by the following.

in controller.php file

function force_login(){
$app =& JFactory::getApplication();
$app->redirect('index.php?option=com_users&view=login');
}

In the above given example, the users will be redirected to URL ==>  index.php?option=com_users&view=login.