How do I create a sub-user?

The person who will receive email submissions as they are completed?

How do I create a sub-user?

Here in JotForm, the sub-user is a feature where you can share the form with another user. You can grant them permissions for your form. The sub-user can view submissions or edit forms. Here's a guide: How-to-Share-Forms-with-a-Sub-Account-User

The person who will receive email submissions as they are completed?

You can setup an email notification so that the recipient will get notified  once a new submissions comes in. Please check these 2 guides:
Setting-Up-Email-Notifications
Explanation-of-Email-Notification-and-Autoresponder-Settings

Let us know if you still have any questions. Thank you.