What is the purpose of "Apply Rules" in mail? The Mail client (that comes with Mac OS X) has an "Apply Rules" menu option, but I don't see any option to create a rule like most other mail clients have. Two part question, what rules does the "Apply Rules" menu option apply, and how do I define new rules in Mail?
To add a rule in Mail, open Mail preferences (Mail > Preferences… or ⌘+,) and go to the Rules pane.



The Apply Rules function applies to all rules whose "Active" checkbox is ticked.