Rules add behavior to forms. For instance, you can add a 
rule that will show/hide certain form controls or entire sections based on the state of other form controls. Displaying form fields in a context-sensitive manner reduces clutter and makes it easier for users to navigate your forms. Rules can also be used to update form values. For instance, you can compute the total invoice price on an order form from values of other form fields such as item quantity and price.
business rules can be created and edited using the Visual Rule Builder or by dropping JavaScript directly into the Rule Validator.