Mailchimp widget fields

Hi, I simply don't get how the newsletter widget works. If I choose mailchimp provider, I only see "form action" box, but where do I put the user and list ID, which looks like this in the source code: <form action="http://mailchimp.us8.list-manage.com/subscribe/post" method="POST"> <input type="hidden" name="u" value="a123cd45678ef90g7h1j7k9lm"> <input type="hidden" name="id" value="ab2c468d10"> Can you help me please?