The Explorer illustrates the hierarchical structure of the current project, containing nodes that represent distinct features and connector proxies.  The selected component can be renamed by clicking on it.  Alternatively, right-click on any node to show its context menu, from which other operations are available.  Double-clicking a node will open the containing view and cause its viewport to pan and zoom to the component represented by the node.

 

The Explorer is shown by selecting View → Explorer from the menu bar or by clicking the Explorer button in the Standard toolbar.