First: Set up the Template

You would need to create the Template which is the actual email message.
You can create one from scratch following these steps Creating Templates

To ensure your email message is compliant, refer to Amazon TOS

Or you can load one already created and TOS compliant from here Prebuilt templates

Second: Set up Custom Campaign

Campaign's use your saved email templates and apply rules and timing to send out those email templates by following these steps: Creating and Editing campaigns

Email Queue

Refer to Email Queue video

To see the status of when your emails will be sent please check the Email Queue page

Inside this page, you will be able to see the shipped and delivery dates for each order and the queued date time which will tell you when the email will be sent based on your campaign timing rules.