How to setup oauth2 youtube api?

Question

YouTube

I need to get information from the channel, or rather a list of videos and information (views, likes, description) in the form of an array. To do this, I decided to use youtube api 2.0, but there is no information at all on the Internet.
I read the documentation on the Google site. got oauth2 ID and key.
I change everything in the siml script presented on the Google site. nooooo it says that the authorization is unsuccessful and the process will not go any further.

who dealt with YouTube api. help me please !!! where and what to read. I do not understand English well, but even in English there is nothing but YouTube documentation.