logout url & session handling

[aniltc]

I have used login url like this
$facebookLoginUrl = $this->container->get('fos_facebook.api')->getLoginUrl(array('redirect_uri'=> $this->container->get('router')->generate('fos_fb_security_check', array(), true) ));

and I have assigned the vriable to twig.Now I am able to login to facebook but no idea what to give for logout.Any one can have idea ? Any idea how to handle sessions after login ? please help me