php sessions...

hey a quick question/clarification... i have the following... <?php session_start(); $_SESSION['foo']; $_SESSION['foo'] = "ffoo"; ?> later in the code i want to use the session var... my question... how/what do i need to use the $foo var. I was under the impression that $foo was automatically available when declaring the session var... do i need to use session_register('foo')? if i do, why... wouldn't the "foo" session var already be registered with $_SESSION['foo'] i have php 4.3.1 arrggghhh..!!!! thanks bruce bedouglas@earthlink.net ps. i've done a google search ..but not quite sure as to how it really works/what's really going on...