Core knowledge points~ 1. Do you know how to plan the overall process of the registration system? 2. How to build a data table 3. How to log in and register with mobile phone number 4. How to deal with multiple registrations by one person? 5. Apply to be a teacher or principal. How to manage multiple roles? 6. Which role is the best to publish the course? 7. How the backend system manages the multi-role platform