In the beginning of your work on the NetBeans Platform, you'll have one module in your application. That's not a modular application! In the screencast, you learn how & why you can modulerize a single module into multiple loosely coupled modules.
A future screencast will show how this is done in a different context, via Lookup and services. In this case, however, we look at how to split the module into multiple modules purely via the System FileSystem, which is the NetBeans filesystem shared amongst all modules in an application, comparable to the Windows Registry, for example.