a. At the highest level (Content Area named "Instructions"), remove the access permission for All Users.
b. In the Content Area "Main Area" assign access permission to All Users.
c. In the Content Area "Private Area" assign the restricted access permissions. Grant permission only to the specific user group.
Note: For details on assigning permissions to users/user groups, see the Administration Guide.
Now you have two Content Areas and within those areas, two libraries. The library "Main Area Library" can be accessed by All Users. The Library "Private Area Library" has restricted access permission but will always load the contents of "Main Area Library".