Setting MailChimp API:
Go to Dashboard >> MailChimp For WP >> MailChimp >> Setting your API Key then click “Save Changes“. To learn how to get API key, you can refer document of MailChimp.
Create MailChimp Form:
Go to Dashboard >> MailChimp For WP >> MailChimp >> Forms:
For more detail, you can read document of MailChimp For WP.