Common Data Service comes with a set of sample data to use for trials and testing. This sample data is small, with around 10 accounts, 15 contacts, and some opportunities, products, cases, and activities.
You can add this sample data from the Power Platform admin center. Open the settings for the environment and expand Data management as shown in the next screenshot:
Clicking on Sample data will open a new window as shown in the following figure:
Clicking on the button will start a series of import jobs that you can monitor for success, as shown in the next figure:
If you want to remove the sample data, then you can click on Sample data and the window is shown in the following figure will open:
You can click on the Remove Sample Data button to trigger the deletion of the sample data...