I am not sure of the exact difference. The ForwardAction is handy when you do not need to perform any logic and just need to display a page. About IncludeAction...my "Programming Jakarta Struts" First Edition book says: "was created to make it easier to integrate servlet-based components" and goes on to say that it provides the same behavior as "using the include() method of a RequestDispatcher". I don't really know what that means but I have never had a need to use ForwardAction.
subject: Difference between Forward Action and Include Action