It is rare to have a class be Private, though it is entirely possible. Normally that is done when the class is defined inside another class, something like this:
Code:
Public Class Outer
 'Stuff for the outer class

 Private Class Inner
  'Stuff for the inner class
 End Class
End Class
In such a case, the Inner class can only ever be created or used within Outer. This greatly limits the versatility and usefulness of Inner, which is why it is rarely done.