The Structure of Past Perfect

Present perfect has many rules. Past perfect is quite not quite simple, but more simple, let's say. The reason why I think it's easier is because there aren't so many rules. So past perfect always uses the word had - if it doesn't have had, it's not past perfect. Another thing about past perfect is it's always used with the past simple. They're never, ever apart. Sometimes we use past perfect alone, but in that case, past simple is implied.