What does the PM function refer to?
The Private Messaging system. You can access it by clicking the "My Messages" link in the blue bar near the top of the OC.net forum screen (in between "Profile" and "Calendar"). We prefer you use this to, say, posting your email, since web bots can indeed pull your email from a public post and then add it to their spam lists. Your email in the profile, and the link to it, are protected from this since only members can view them.