There are several samples that use the Common Data Service. To find these samples, on powerapps.com, select Home in the navigation pane.
There are several videos that demonstrate how to create and modify a database, and how to create apps. You can find these videos in the documentation and you can also find them on powerapps.com. Select Home in the navigation pane and look in the Use the Common Data Service section.
You can find how-to posts on the PowerApps blog.
Many sessions of the Microsoft Ignite conference were recorded and are available at Microsoft Ignite On-Demand. Search for "PowerApps" and "common data model."