This document discusses API driven development in Moodle and how to build API endpoints. It covers registering API endpoints in Moodle's external service description, creating external functions to define the API, and making API calls. External functions define the parameters, return values, and business logic for each API endpoint. The document provides an example of an external service description and external functions for a get_quiz_questions API. It emphasizes the need for security and monitoring when building APIs.