See Also
One way is to use modules is to start at the top by determining the connections between modules and then creating the contents of each module. This method is called "developing the dynamic hypothesis". With this method, you first look at the connections between modules, envisioning the overall flow of information from one module to the other. Only after you've made a plan for how each module is connected to the other do you start building the contents of each module. The airline module example shows a module that is built this way.
Another way is to use modules is to use (or re-use) an already-built structure in your model, or to hide the details of a complex process. With this method, you are using the module to perform a function in your model. You may not have built the module yourself, and you may not even be able to see the details of the module if it is locked, but you have access to the module by providing input values to the module and retrieving output values generated from the module.
Use modules to communicate between modules
Use modules to re-use a common structure or hide a complex process