We use the past simple when we are talking about an event that happened at a particular time in the past or something that continued for some time in the past:
We drove home before midnight.
They worked little through the summer.
When we are looking back from a point in the past to something earlier in the past we use the past perfect:
Jack suddenly remembered he had left his mobile in the car.
|Past simple||Past perfect|
|Past simple (second column of the irregular verbs list or by adding -ed to the regular verbs)||Had + past participle (third column of the irregular verbs list or by adding -ed to the regular verbs)|
|AFFIRMATIVE||Janice saw the advertisement on TV. (see – saw)
They lived together last year. (live – lived)
I had seen the movie before.
(see – seen)
She had watched the movie three times. (watch - watched)
|NEGATIVE||My mother didn't want to go to the beach today. (did not want)||
My friends hadn't arrived to the party by the time we got there.
(had not arrived)
|QUESTIONS||Did you like the film?||Had she spoken to James?|
Note that, when adverbs such as never, just, already... are added to the past perfect sentences, they are placed between had and the past participle:
When Jane went to see the elephants, she had already seen the lions.