If you'd like to integrate Mailchimp, just follow these steps:
- Add a form 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
Don't know your API key?
See here on how to find it - http://kb.mailchimp.com/integrations/api-integrations/about-api-keys