Past Perfect tense is used to describe something that happened in the past before another past event and Past Perfect Continuous to say that something had been happening for a period of time before something else happened. Examples: When we got home last night, we found that somebody had broken into the flat. ( first somebody broke into the flat and then they came). 2) When the boys came into the house, their clothes were dirty, their hair was untidy and one of them had a black eye. They had been fighting. ( They had been fighting and that's why their clothes were dirty) 3) Yesterday morning I got up and looked out of the window. The sun was shining but the ground was wet. It had been raining. (It was not raining when I looked out of the window; the sun was shining. But it had been raining before and that's why the ground was wet.) I hope you can now see the difference between PP and PPC