Make sure that you complete building your site in Affilojetpack before proceeding with the following steps.
Login to your Fluttermail account and click on the Integration tab.
Click on the Create New Form button on the right sidebar.
Select a list for the form by clicking on the drop-down menu, then give the form a name and click on the OK button.
Click on the Opt In Confirmation Email button and change the From Name and From Email Address. You can choose to edit any of the other elements on the confirmation email (subject line, content, etc) but DO NOT edit the Confirm My Subscription button on the body of the email.
Click the Save button on the top right of the page to save the changes.
Click the Integration tab again and copy the Form ID under the form you created.