Arena provides a way to encapsulate different parts of a model, a submodel. New submodels can be added by using Object > Submodel > Add Submodel. A new submodel can also be added by clicking on the Submodel button. The submodel can then be named by right-clicking and selecting Properties....
You can open a submodel by double clicking on it. You will then see a new flowchart view (representing the model within the submodel) with entry and exit points. These points correspond to the entry and exit points on the submodel module in the main flowchart view.
You also can "nest" submodels within other submodels.
The easiest way to find your way around your submodels is using the Navigate template.
The attached flash movie shows how to create a submodel and navigate around it:
-- MichaelOSullivan - 25 Aug 2009