First, create a form report using the Form Reporting function. 

You can get to the Form Reporting page by using the dropdown menu to navigate to Forms => Form Reporting:

Here you can select the form template you wish to report on, the columns it should include, and any filters. 

The report that this creates are often referred to as “CSV Reports” as their original function was to create an easy CSV export of form data.

Creating a CSV Report in more detail:

Once your report is configured, you can view it on the Manage CSV Reports page, found by clicking the “Manage CSV Reports” button near the top-right of the page.

The Manage CSV Reports page lists all of your available reports, and exposes an API link that can be used to access data from that report from an external service (such as Power BI).