By default Mokoala uses the 'mk' namespace for sessions, which is the equivalent of storing all $_SESSION data within $_SESSION['mk'].
All session data is controlled through the MK_Session class. The below example would store 'some text' to $_SESSION['mk']['my_value'].
MK_Session::start('mk');
$session = MK_Session::getInstance();
$session->my_value = 'some text';
To delete data simply use unset().
MK_Session::start('mk');
$session = MK_Session::getInstance();
unset($session->my_value);