there isn't really a lot to know about setting up postfix what distro are you useing, you might want to setup webmin, that has an exellent postfix web interface, if you just start postfix, start dovecot (or whatever imap/pop server your using) and start apache.
Then you should be able to login to squirrelmail with any local user name and password.
start looking though your /etc/postfix/main.cf file
you also might want to have a look at this
http://www.yourhowto.org/content/view/33/9/ - pop3 Server On Fedora with IlohaMail
http://www.yourhowto.org/content/view/55/9/ - Dovecot imaps/pop3s with openssl and squirrelmail
there is a bit of information on my website listed below if you want to look around that to see mail server setups.