How can we add an email?

I presume that you are looking to add an email notification to your form, but if that is not what you mean, then please do let us know about it with a bit more details on what you are after.

Now to add the email notification, you should take a look at the following guide: Setting Up Email Notifications

If you were actually looking on how to setup the email to be sent to people that have submitted the form, then I would suggest taking a look here instead: Creating a Form Autoresponder