The Project Explorer view shows all the projects in you workspace and the files they contain. It adds some special capabilities to modeling projects to allow you to view and manipulate your semantic models and their diagrams.
The Project Explorer supports the Link with Editor feature, which can be enabled by pressing the icon in the top right corner of the view.
If you enable the Link with Editor and click anywhere on the opened representation, then it will automatically select the corresponding representation inside the Project Explorer (expanding the project and files, if necessary).
Conversely, if you select a semantic element from one of your semantic models in the Project Explorer view, and if this element is represented somewhere on the opened editor, it will be automatically selected.
This feature can be very useful when you have many projects and representations, or large representations.