This feature was created to help support course creators who want to manually add customers to a course (without that user having to do anything at all!)
If you have many customers to import in bulk, please see this help doc.
Make sure you're in the Teach section in the top nav bar
Click Customers in the sub-nav menu
Click + Add Customer to Course or Theme button
Enter the customer's First name, Last name, Email, and then select the Course or Theme from the dropdown menu
Click the + Add customer button and they'll be added*! 

Or just want to test out how your course flow looks?
You can also use the Add Customer to Course or Theme feature to quickly add test customers or yourself. Itβs a simple way to give someone access to your course without having to create a Landing or Payment Page.