Enable email notifications
At the top menu bar of the form builder click
Style & settings. The Style & settings pane will show up on the left side of the form builder.
On the left side of this pane you can enable the feature
Notifications - Email. After enabling this feature you can enter the email address of the recipient. This will result in a simple email message to the entered recipient when someone completes the form.
Include response data
It's also possible to include all response data of the completed form directly inside the email message. In that way, you don't have to open up your WP Admin to see the given answers. To do so, just enable the checkbox
Include form data and all given answers will be shown in the email message automatically.