Hi Unfortunately I have been trying to open the UML diagram on the right hand side editor by double clicking or Dragging on the Diagram Shortcut under Model window. However no UML diagram is shown in the main window. I a first time user. Kindly help. Attaching the screenshot for reference.

Am I doing some wrong steps? Basically I want the complete picture in the main window so that I can understand project.

Hello,

The diagram is open but contains no element.

You can either use the diagram palette to create content, or drag&drop elements from the Model view to the Diagram view.

How does it help?

Thanks Osl. Just to give more background this piece of model has been auto created by reverse engineering of Java code. I was under the impression that by clicking or dragging the Diagram shortcut as mentioned in earlier screenshot we can get the complete UML diagram and their link.
However if I get your point correctly it is not the case. We will need to individually drag those diagrams into the Diagram view and then create their relationship.
I have attached the diagram as an example.
Can you please confirm if this understanding is correct?
Cheers,

Your urgent reply to my above query will be really helpful.

Yes, you have right.

You drag & drop elements you want to see from the explorer to a diagram.
In the "Symbol" tab, you can unmask some elements (eg. attributes, operations) automatically.

In the context menu (from an element in the diagram), you have shortcuts to unmask some linked elements.

Modelio can also create diagrams automatically after a Java reverse to understand the structure of your model: See this post.

Ok. Thanks TMA.