• A period is attached to the present moment:

    • The Present Perfect Continuous Inclusive.

      He has been sleepping for three hours.
      Он спит уже три часа.

    • The Present Perfect Inclusive.

      I've known him for ten years.
      Я знаю его десять лет.

  • A period of time is attached to a definite moment in the past:

    • The Past Perfect Continuous Inclusive.

      She said that he had been sleeping for three hours.
      Она сказала, что спит уже три часа.

    • The Past Perfect Inclusive.

      She said that she had known him.
      Она сказала, что она его знает.

  • A period is not attached to any definite moment.

    When I was a child, I lived in this town for several years, that's why I know it well.
    Когда я был ребенком, я жил в этом городе несколько лет, поэтому я хорошо его знаю.

    When a period is not attached to any definite moment, the action is regarded as a simple action in the past and it is usually expressed by the Past Indefinite.

    Yesterday I played the piano for two hours.
    Вчера я играл на пианино два часа.

    Note: The Past Continuous can be used emphatically to emphasize the duration of an action.

    I was waiting for you at the entrance to the metro station for a whole hour yesterday.
    Я вчера ждал тебя у входа в метро целый час.