The short answer to "How do I use Pine on the Mac?" is that you really can't.  The new accepted terminal-based e-mail client is Alpine -- it's free and open, unlike Pine which is not and is being discontinued.  They're about the same thing functionality-wise, it's just Alpine will continue to be updated.

That being said, if you're running MacOS X 10.4, you might try MacPine, a binary provided by the University of Washington:

MacPine: http://staff.washington.edu/jdlarios/MacPine/

If you're running MacOS X 10.5, you can download Alpine from the Apple Download site:

Alpine: http://www.apple.com/downloads/macosx/unix_open_source/alpineemailclient.html

Configuring Pine/Alpine for DavisMail:

1. In your DavisMail preferences, enable POP or IMAP access under 'settings'
2. In Alpine, go to Config, and set your inbox-path to the following (pop/imap, POP3/IMAP4):
3. {pop.gmail.com/POP3/SSL/novalidate-cert/user=YOUR-EMAIL@gmail.com}INBOX
4. In Alpine, configure your smtp-server as follows:
5. smtp.gmail.com/user=YOUR-EMAIL@gmail.com/ssl/novalidate-cert
6. Save settings and restart Alpine.