Every time you perform a Go To or Visit To operation on
  a help topic, the topic title is recorded in a history
  list.

  The Go Back button and the Go Back item of the View
  menu use this history list to display each previous
  topic as you request it.

  You can also access the history list through the
  History... item of the Search menu. The History... item
  lets you return quickly to a topic that is far back in
  the history list.