Where would there be basic instructive details for users with rather spotty levels of expertise, little expertise, no expertise about how to compose, setup dotfiles for filtering Rmail spamassassin tags?... the ideal would be instructive details that explain line by line, expression by expression what would be included in a dotfile for filtering and what each expression, how each term will act.
Reference For Rmail users where spamassassin tags appear on messages already, here are hints, tips and pointers about how to filter http://www.emacswiki.org/cgi-bin/emacs/Rmail