Suppose your client wants to offer their site members some exclusive content; anyone registering to the CORBA site can read all about exclusive club meetings. Let's make sure the content shown through the Activities | Club Meetings menu link is displayed only partly—unless users register:
Make sure you're logged in to the backend of the site as the Super User. Open the current Activities menu link (Menus | Main Menu) to edit it. Make sure the link itself is visible for all—the Status should be Published, the Access should be Public.
Under Advanced Options | Article Options, 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. Save & Close the menu link.
To set the access level of the desired articles to Registered, navigate to Content | Article Manager. In the Select Category...