It is used for actions that start in the past and continue up to a given time in the past:
- I had finished the article when they said it was dinner time.
- Yesterday evening at nine o'clock I had already finished the videogame.
- She hadn't arrived when we phoned.
Also in 3rd type conditional sentences:
- If you had asked me, I wouldn't have let you go.
- We wouldn't have solved the quiz if they hadn't helped us.
- Perfect English Grammar
- Ego 4 You
- Oxford University Press
- Englisch Hilfen - statements
- Englisch Hilfen - negatives
- Englisch Hilfen - questions
- Englisch Hilfen - mix