How can I reply to the person who filled the form?

We have a registration form that includes a required field for an e-mail address.  I would like to be able to reply directly to those people when we receive the e-mail of the form submission.  I understand the "sender" line in the e-mail setup needs to be the Jot-form one, but if I put the "e-mail" field on the "reply-to" line, will that give me a reply-to address that I can have an automatic reply to?

Yes. You can select the existing email field where your user fills in their email as reply-to address. You'll be able to reply to the users email id by adding this field. However, please be noted that some of the email clients such as Microsoft Outlook, etc are not supported with this feature and they doesn't display reply-to email address.

On the other hand, if you want to send auto reply to your users when they fill your JotForm you may consider using adding Auto-Responder. 

http://www.jotform.com/help/26-Creating-a-Form-Autoresponder

Hope this information helps. Please get back to us if you need any further assistance.

Thanks!