I have a question about this line

[usamusa]

You can use wherever you want to manipulate page content depending on wether the user is logged in or not,

Code:

<?php if(isset($user) && $user->isLoggedIn()){ ?><P>You are logged in</p>
<?php }else{ ?>
<p>Not logged in</p>
<?php }?>

or to manage access to pages. I usually use the admin dashboard for that though.
It's very flexible really, but The only lines that you have to include in custom pages are:

Code:

<?php require_once 'PATH/TO/init.php'; ?>
<?php require_once $abs_us_root.$us_url_root.'users/includes/header.php'; ?>
<?php require_once $abs_us_root.$us_url_root.'users/includes/navigation.php'; ?>