Click the 'Blue +' Add a 'Form' stripe to your site
Click on 'Send'
Choose 'Add User To A Mailing List' from the drop-down menu
Click on 'Configure'
Click on 'Settings'
Click on 'Setup'
Choose Mailchimp from the drop-down list
Enter your Username and API Key.
*As well as Mailchimp, you can also connect to Getresponse & aWeber with the same process detailed above.