Newsletter
Connect Mailchimp
Go to Mailchimp and create an account.
Create a new list in Mailchimp https://us20.admin.mailchimp.com/lists.
Go to Account -> Extras -> API keys https://us20.admin.mailchimp.com/account/api/.
Copy API key and paste to Admin -> Settings -> Newsletter -> Mailchimp API key.
Copy List ID and paste to Admin -> Settings -> Newsletter -> Mailchimp List ID, then click Save. Or just click Save setting, and it will auto get List ID.