Each item on the website, as entered by you or your staff, can be marked as to WHO can view it.  Most information will be for the world to view even when they are not logged in.  But you can restrict certain items so that only certain users can see it.  For example, say you have an event that is a Staff Meeting.  You can mark it so that it only shows up in the events when a staff member is logged in.  Other items can be marked for Members Only.

There are many features that cannot be seen on this website unless you are logged in.  The ability to add/edit/delete items, such as news or events, exists for those who have been given privileges to be able to do those tasks.  Each user can have unique privileges regarding their ability to add/edit/delete site content.