Every time you perform a Visit Topic or Go To Topic
  operation on a help topic, Help records the title. The
  list of titles that this creates is called a history.
  The Go Back button and menu item use this history to
  display each previous topic as you request it.

  You can also access the history through the history
  menu item of the Search menu. This enables you to
  quickly return to a topic which is a long way back in
  the history list.