YITH WooCommerce Membership is a plugin that allows you to organize the content of your site into plans and make it accessible only to users who have paid for it. With this plugin, you can offer your users a wide selection of products in exchange for a cost.
The combination with YITH WooCommerce MailChimp the admin can set up Mailchimp lists in the membership plans. So when a user becomes a member they will be added to the selected Mailchimp list.
To do that, just make sure you’ve installed and activated both plugins from the Plugins menu and configured both plugins based on your needs.
Then, open a membership plan: you’ll see a metabox on the right side, called MailChimp, where you specify the list to which users have to be subscribed whenever they have this membership plan activated.
Also, you can enable or disable the checkbox in the same metabox: Unsubscribe when expired or cancelled. If you enable this option, every time the membership expires, the user’s email address will be removed from the related MailChimp list. If disabled, the email address will be kept even if the plan expires or is cancelled.
For any further details about YITH Membership, please, refer to the official documentation here.