where do completed forms go

Once the form submitted, the submission data sent to your account's Submission page. And if you set up any notification email data will be sent to your email as well.

Follow this guide to know how to view all your submission data: https://www.jotform.com/help/269-How-to-View-Form-Submissions

To set up Autoresponder and Notification Emails: https://www.jotform.com/help/30-Explanation-of-Email-Notification-and-Autoresponder-Settings