[JDEV] Roster vs. Presence

[Paul Vet]

OK, I'm a newbie to Jabber, although I'm looking into playing around with
developing a client.  I just want to clarify what a roster/presence is/are.

Let me make an ICQ comparison.  When I add a user to my Contact List
(Roster?) it sends a request to that user.  If they accept, the server then
sends me online status info (Presence?).

To do the same process in Jabber, what is necessary?  I see a <presence>
subscribe action, and there's seperate roster stuff.  So to get the full
functionality of a user, do I add them to the roster, then send a presence
subsctiption request?

Thanks,
Paul