Hi imparare, the confusion is understandable, but I am not sure how to explain this.
Check out any ‘old way’ Texture Paint tutorial (2.79). You’d create a texture in the UV/Image Editor. Add an Image Texture Node in the Node Editor, with the same name as texture you created. Made sure that that Image Texture Node was selected and the Material assigned to the Object you wanted to paint. In the 3D View go into Texture Paint mode and you could start painting, both in the 3D View and in the UV/Image Editor.
Now (in 2.80), you can go into Texture Paint workspace and create your texture where you said, and everything that you had to do by hand is now done automatically. Even a Material is created if not already there…
Hope this makes it a bit less confusing.
