Scripture, Tradition and teaching authority
The apostolic faith is handed on through Sacred Scripture and living Tradition. The Magisterium, the teaching office of the pope and bishops in communion with him, serves that inherited faith. It does not create a new revelation. Different kinds of teaching carry different authority. A doctrinal definition, a disciplinary decision, and a personal theological opinion should not be treated as interchangeable.
Follow the sources
An original library introduction, with sources for further study. This is a starting point rather than a complete treatment or a finished formation lesson.