SESSION doubt

I am learning PHP, today, i got a doubt about session,,,,,

here is the code

	session_start();

	if ((isset($_GET['action'])) && ($_GET['action'] == 'true')){
		$_SESSION = array();
		session_destroy();
	}

PHP:

first session is started using "session_start()" function,,,

i cant understand next two lines, can anyone please explain

 

if condition checks whether "action" parameter received using GET method of HTML is set or not. IF it is set, assign a blank array to $_SESSION and destroy the session after that

 

can u please say what is the use of assigning a blank array for $_SESSION

 

its for resetting the $_SESSION

To cleanup session one can assign a blank array to it

 

thank you very much