Hi Viktor,
Model Explorer lists the model elements in the model repository, while Diagram Navigator lists the diagrams and the diagram elements within each diagram.
You can think of a model element as the data of something that you want to model, like a class named “Car”. A diagram element is a representation of a model element (also called a “view”), take the “Car” class example, it can be a class shape shown in UML class notation, or it can be shown as an image of your choice.
Hope this helps,
Antony.
