For an add-on, the "log in" is done during the installation process. For an add-on, it's not really "logging in" in the sense of creating a user name and password, but they insist on using that terminology. I guess that the user is logging in through their existing Google account.
I found that part confusing.
Also, the client ID is shown in the address bar of the authorization window. And it's very long. You will need to widen out the authorization window in your video in order to show the entire client ID. The client ID is automatically put into the url in the authorization window.
I wouldn't go into complete detail of showing how to use every possible aspect of your UI. My video would be hours long if I did that. Any parts of your UI that are directly related to some other scope I would explain.
How to request an Auth token. The user doesn't explicitly request an Auth token. That is handled by the add-on authorization acceptance. All they do is either click the Accept button or not. But, in my video I explain what each of the asked for permissions is for. And if the add-on does not use some part of the permission, like delete all your files in your entire Drive, I assure the user that the add-on doesn't do that.