Say for e.g. we want to hide Test Page navigation link from the Portal for anonymous users and make it visible only for authenticated users.
For this we can create a Web Page Access Control Rule,
Go to Portals à Web Page Access Control Rules and create a new rule as shown below
Select the Website and the web page to be hidden.
For Right, select Restrict Read and in Web Roles add Authenticated Users Web Role.
On refreshing the portal à
For logged in user
For anonymous user
Hope it helps..