The Previews button allows you to interactively preview the app in a simulated device browser. You can interact with the application as if it was a live app on various simulated platforms.
For each preview, adjust the Width and Height value in the left pane, and interactively view the changes in the right pane. In addition, rotate the view by clicking the portrait or landscape button in the upper-right corner of the preview window. Once completed, click Configure to return to the configuration page.
Further, you can scan QR code to view the app on your mobile device.