// login, set session variable to TRUE
session_start();
$_SESSION[ 'is_logged_in' ] = TRUE;
////////////////////////////////////////////////////////////
// any page where check if logged in
session_start();
if ( $_SESSION[ 'is_logged_in' ] === TRUE )
echo 'you are logged in';
////////////////////////////////
// logout page. 'logout user', unset session variable
session_start();
unset( $_SESSION[ 'is_logged_in' ] );
echo 'you are no longer logged in';
notice, at any page you want to work with current session variables
you have to start the current session = session_start();
Session variable will last, as long as user has his browser up.
When he closes his Internet Explorer down,
session is ended and SESSION variables are deleted.
