Scenario
In this post we will see how to create a PowerApps environment with connected database of Common Data Service (CDS) containing only the core entities defined by the Common Data Model (CDM) to store the data of your apps.
Solution
Go to the PowerApps Admin Center portal https://admin.powerapps.com, select Environments from the left panel and then select New Environment on top right.

Into opened popup enter Environment name, Region and Environment type (Trial or Production), then click on Create environment.

At the end of the creation process, you are asked whether or not to create the database associated with our CDS, select Create database.

Specify your Currency, Language and whether or not to include demo applications and sample data, next select Create database again.
Now on the PowerApps environments list we able to view the environment just created.

To view the CDS database connected to our environment with only the core entities of the CDM, now we go on PowerApps portal https://web.powerapps.com and select the created environment from the top right panel.

Expanding from the left panel first Data and after Entities it is possible to display all the core entities prepared by the CDS.

These represent all the core entities of the CDS database on which our Model-driven apps and Canvas apps will work.
Very important, also Dynamics 365 Customer Engagement apps (Sales, Customer Service, etc…) will use this database and these entities :-)!
Hope it helps and happy 365Power’ing!