This book is aimed at educators. Moodle uses the term 'teacher' to describe someone who hands out and grades work. But, as far as Moodle is concerned, you are only a 'teacher' when you are in a course in which you are handing out work and grading it. In Moodle-speak, you have the role of 'teacher'. It is a mistake to think that just because you are a teacher (i.e. that's your job) when you are logged into Moodle you will be a teacher in any Moodle course. That's like saying you could walk into one of your colleague's classrooms and start taking their lesson. Well, you wouldn't do that and it's the same principle in Moodle.
In the normal scheme of things, the person who makes you a teacher in a Moodle course is the person who created the course—usually your Moodle admin. It may be that you've been given the task of creating courses. That's the role of the Moodle 'Course creator'. They can create courses and assign roles. Interestingly...