When you install a Dynamics 365 app for the first time, a new environment and database are created. The database schema is created using the schemas in the CDM.
What's important as far as the rest of this book is concerned is that customizing Dynamics 365 apps is performed by customizing the CDS that the Dynamics 365 app runs on.
For the purpose of customization, you can think of a Dynamics 365 app, such as Dynamics 365 Sales, as just a model-driven app. It has the same customization and extensibility capabilities as any custom model-driven app that you create. You can build new apps against the Dynamics 365 entities or add entities to the Dynamics 365 apps.
There are some technical details as to how the CDS is implemented that you need to be familiar with.
