Each folder in this repository is a separate solution for a given problem (what is a problem is a separate issue). So for information on the solution to a particular problem, go to the appropriate folder and find its README.
Since the solutions are posted for YouTube Data API (v3), you need to create (have) a Google Account, a Google Developer Profile, in Google Cloud create a project, and enable the API in the project. In order to do this, you can go here.