Suppose your client wants to offer their site members some exclusive content; anyone registered to the CORBA site can read all about exclusive club meetings. Let's change the settings so that all content shown trough the Activities | Club Meetings menu link is displayed only partly—unless users register. The steps are as follows:
Make sure you're logged in to the backend of the site as Super User. Open the current Activities menu link (Menus | Main Menu) to edit it. The link itself should be visible for all; Status should be Published, and Access should be Public.
Under the Options tab, set Show Unauthorised Links to Yes. This is the step that takes care of the "register to read more" magic. Of all articles that have been assigned Registered status, only the intro text will be displayed. Click on Save & Close to save and close the menu link.
To set the Access level of the desired articles to Registered, navigate to Content...