Sorry, but the documentation does make sense, also it is a standard OAuth2 as stated in the very end of the API docs Using OAuth section. It should be really simple to implement in most scenarios.
Without knowing details of your project (like the programming language you are using, or how you create the token) it is impossible to guide you to a better experience.
I would recommend you joining the Blizzard API Community Discord Server and sharing with us more details so we can point you in the right direction.