A link in a navigation model is more than just a link as you would expect. A link in a navigation model can be a lot of things. It can be a link to an external application, page, taskflow, portlet, and so on.
You can also specify to render the link in a specific page template. This way you can add links to taskflows or external pages but still keep the look and feel of your portal.
For this recipe, you need a WebCenter Portal application.
idfor the link. This must be unique within the navigation model.