How do EZ-Pages work?

[ckosloff]

I am trying to implement the "correct" way of linking within EZ pages.
So I did:
<a href="<php echo zen_ez_pages_link(15,2); ?>">Read more...</a>
and got a 403 Access Forbidden error on my test site.
Now, when I do my "incorrect" way:
<a href="index.php?main_page=page&id=15&chapter=2">Read more...</a>
it works.
Please explain.
Thanks.