Before you can define a navigation link, you must create an outbound plug for the start view and an inbound plug for the subsequent view.
See Creating a Plug
You create a link to implement the navigation between two views of a Web Dynpro application in the graphical Navigation Modeler tool.
In the Navigation Modeler, the link is displayed as a line between the outbound plug of the start view and the inbound plug of the subsequent view. In the Web Dynpro Explorer, the navigation link is displayed as an entity of the outbound plug.