I'm also looking for information on how to configure SpamAssassin. The internet seems to have nothing on it.
I have installed it and it seems to work (with defaults) for my email account, but it does not scan my wife's email account that is on a different domain on the same server.
The file /etc/mail/spamassassin/local.cf does not seem to be the correct config file either. Any changes I make in there don't seem to have an effect (the tag added to the subject line of a spam email is different, for example). I did use "Restart all Mail Server Services" button on the Postfix manager page after making a change in that file.
Does anyone know what the correct config file for SpamAssassin is when it has been installed through the Postfix manager?