cannot store / write sessions

Hi

I'm trying to set sessions based on the post then use them later, any idea why this does not work.... and is this a security risk?

if it is a rick, are there better ways or something else I should add to check on

Thanks
Neil

session_start();
foreach ($_POST as $var => $val) {
   $_SESSION[$var] == $val;
   echo $_SESSION[$var];
}