So in your first image, the reason the mask now appears to be affecting everything is because in the Image slot, it has been set to a uniform value of white (100%). This essentially means that the model is being filled with the mask entirely since there is no variation in the mask.
You will want to set it to another image of some type, like the Ring texture that we use in the lesson.

As for the Layering Project tutorial, it likely shouldn’t be anything that is conflicting with what you are trying to do! You should be able to dismiss it if you find it is impeding on your UI, but there will be no effect otherwise.
Sometimes a fresh working file is all you really need for things to start working properly again! If you are already starting anew, just keep in mind some of these troubleshooting options for when you get back to this part of the lesson, and perhaps can even try it early to make sure there’s no surprises. 🙂