Export client information to MailChimp. Reduce the data you have entering and maintain the accuracy of your automated email messages. This connection will automatically export new customers' information to your MailChimp subscriber list as they sign up:
Go to the "Integrations".
Click on "Mailchimp".
As seen in the screenshot linked, you must export data using Mailchimp in this case. Additionally, go to http://mailchimp.com to access your Mailchimp account. Put in your Mailchimp listed ID and API key.