how to create signup form with MailChimp module
I get it. You’ve just signed up for Mailchimp and set up your first list. You want to put a signup form on your Drupal 8 (probably works in D7 as well) website so visitors can start signing up for your newsletter or announcements. Here's how you place a signup block. I know this is a late answer, but hopefully it will help someone. To get through this process you have to clear cache a lot. Here's what worked for me.

Install and enable the mailchimp module and the Mailchimp_signup module. Set up the API key with your mailchimp API clear cache (on the command line you can type ‘drush cr’ or you can do it in the admin menu | config page | performance link | clear all caches button).

Go to admin/config/services/mailchimp/signup and add a signup form. Give it a name and remember the name since that’s what you’ll search for when you’re ready to place the block. Check the ‘Block’ checkbox. Choose at least one list that you’ve set up on Mailchimp’s website or on the Lists tab. Save the form.

Refresh cache ‘drush cr’ again.

Go to the Structure | Block layout tab. Choose a region where you would like the signup tab and choose ‘Place block’. Search for the name you used when naming your signup form. Choose it and ‘Save block’.

Now go to your site and observe your work. Your form will appear in the area you specified.