Spamassassin - the quick and dirty how-to?

I've had it! I've been spammed to the point that I don't even want to look at my mail. I want to set up spam assissin, or similar to kill all spam. I don't want to spend a lot of time on this. Is there a quick and dirty guide to getting it working? I have my own sendmail server as well as an account with my ISP, I pull my mail from the servers using fetchmail. My mail box type is what KMail calls "local" and it looks as though the queue is /var/mail/$USER. I usually read my mail with KMail. I don't know if spamassassin will execute independently of KMail, or as a script invoked by KMail. Yes, I will be looking at the docs, but if there is a simply three sentence howto that covers my situation, I'd love to see it. STH