Some notes to make it easy to understand when to use this tense

1. Past Perfect
A brief guide

2. It is used to express:
- past actions referred in the past:
He told me he had suffered a lot
- historical events in connection with
others: First he had given a coin and then a note
- narration: He had married four times

3. Interrogative form
Where had you been before you entered your flat?

4. Negative form
I had not done anything special before I entered my flat.