Past Perfect

The past perfect tense, also pluperfect tense, is used for actions that took place before a certain point in the past. It is often used together with the simple past tense.
We use this tense to express:
actions that took place before a certain time in the past
Example: Little Miss Muffet sat on her tuffet after she had made herself some porridge.
the third conditional
Example: If the spider had not frightened her, she would have finished her porridge sitting on her tuffet.
The signal words for the past progressive are listed below: already, just, never, not yet, once, until that day etc.
To conjugate the past perfect tense in English, we follow the rule: had + past participle.