Follow step 1 to 4 in the above picture, open MailChimp's website.
Log in yourself and authorize OCP.
The page will then bring you back to OCP. You can see your account name now.
In your Action step, find "MailChimp" in the "Integrations" list.
Simply put this Action after a Question step. Pick a MailChimp list and put users' email address. That's all about it!
Let's see what happen in MailChimp:
In your MailChimp dashboard, click area 1 and 2 from the left sidebar. Then you will see the audience added from the source OCP.
More details click -> Mailchimp