May I know what are the step to run spam assasin in Redhat Linux
You've probably sorted this out for yourself by now (or left in despair), but here's the information.
1. You don't have to turn spam assassin on: it runs automatically.
2. Marking an email as junk will enable the program to learn: if it has any suspicious feature, then spam assassin will pay more attention to that feature in future.
3. Look at ~/.spamassassin/user_prefs
This is where you can add your own configuration, by making any particular test more sensitive, lowering the threshhold for marking a suspect email as junk, or even adding your own tests. I have added
body ADOBE /adobe/i
score ADOBE 3
body RETAIL /retail/i
score RETAIL 3
to catch people offering me pirate copies of Photoshop!
See the instructions at spamassassin.apache.org