Have you ever thought about incremental development model, which can give you working software every two or three weeks? Agile implements this kind of approach. Actually Agile is a set of software development methodologies that implement iterative highly effective methods. Most popular of them are SCRUM and Kanban.
Agile coaching is a way to implement Agile in the organisation. This is more then only training or teaching people. Agile coaching is about inspiring IT people to implement Agile in their organisation. And it's true because if you only want to know the basis of Agile, read a book. If you want to adopt Agile in your company, you need Agile coach.
We don't only teach people, we coach them and inspire them to improve themselves and there organisation.