Install MailChimp for WordPress plugin
Connect the plugin to your MailChimp account
Create your lists in MailChimp
Create a form and select the list
Edit the form and Add the form with the shortcode
We use this form html for our form from demo.
COPY the mailchimp_form from this URL.
Replace the form in the shortcode example from demo content or add in a different text shortcode in a different location