If your have your own form implementation you're satisfied with on your website you can connect it to your account by clicking on the connect tab.
This will allow you to add your opt-in subscribers from your form to a contact list, automated email sequence, tag them, and view your conversion rate and visitor statistics in your account.
Implementing your own form connection requires some basic HTML abilities, if you need any help just open a support ticket and we will assist you in getting it setup.
Connecting your own form makes the Design tab and Display tab inactive, ignore those tabs for connected forms
