I just set up Mailchimp with my wordpress site, so it's still new with me. However, I'm not sure I know what you mean by an email submit button. I have Mailchimp up on my site to create a list of subscribers to that site. If this is what you are referring to, you go to LISTS in the main menu, and then DESIGN SETUP FORMS. Once you create the form, you can copy the code, and put it into a widget in your wordpress site, and it will show up in a sidebar.