Selecting the Create Submodel item as shown above will display the dialog below:

From here you can select tables that you want to include in the submodel.  For those not familiar with data modeling, a submodel is a smaller view of your overall data model that normally corresponds to a particular functional area.  For instance you might have a database for customer ordering.  Within this database might be tables for tracking customers, contacts, payment history, credit status, addresses, contact numbers, etc.  There might also be tables representing orders, products, inventory status, vendors, shippers, etc.  This can get to be a large number of tables very quickly and would be very diffuclt to manage and model effectively if treated all at the same time.  Submodels allow you to split a particular subject area into a workspace to work on it separately without all of the clutter of the master model.  This gives you a small group of tables that is much easier to manage.  Unless you are designing small databases, you will use submodels very extensively.

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