These two tenses are both used to talk about things that happened in the past. However we use past perfect to talk about something that happened before another action in the past, which is usually expressed by the past simple.
"I had already eaten my dinner when he called."
In other words, First I ate my dinner, then he called.
The past perfect is often used with already, yet, just and even.
In the following sentences, do we need the past simple form of the verb, or the past perfect? The first two questions should remind you when we use each tense.
Note on questions 3 & 6: There is a possibility of both being correct BUT as we have two actions in the past and the homework happened first, it is better to use past perfect
Today's lesson is by Caroline
Link: Can you name the tenses?
Link: Verb Tense Review