Here are the notes about the Past Perfect that I showed you:
PAST PERFECT: We use the past perfect (had + past participle) to talk about time up to a certain point in the past.
Past perfect for the earlier of two past actions
We can use the past perfect to show the order of two past events.
The past perfect shows the earlier action and the past simple shows the later action.
Examples:
The thief had escaped when the police arrived.
When the police arrived, the thief had escaped.
The thief had escaped when the police arrived.
When the police arrived, the thief had escaped.
Here's a link with more notes and exercises to practise the Past Perfect.
See you!