How to log in to api using Auth2.0?

Question

PHP

There is a system documentation:
https://api.glueloyalty.com/#c28c3801-1069-4a3f-a5...
To access api methods, you first need to log in via Auth2.0, but I don’t understand how to do this.
I understand that a person must first register on my site, then he is assigned an individual identifier (client_id), then I use the api method - Get Authorization Code and enter my data there? Am I thinking right? or somehow differently?