The Past Perfect Simple tense is used to describe actions that were completed before another point in the past. It uses the auxiliary verb "had" plus the past participle of the main verb. Some examples of its uses are to describe an action that was finished before a specific time in the past, or an action that was completed before another past action. Time expressions like "before", "by the time", and "already" are often used with the Past Perfect Simple tense.

1. S
Past
Perfect
Simple

2. Structure (Form)
Structure
Auxiliary Verb: Had
Affirmative
Subject + Aux Verb + Past Participle
I had worked
She had slept
Negative
Subject + Aux Verb Not + Past Participle
I had not worked
She had not slept
Question
(WH Question) + Aux Verb + Subject + Past
Participle
(When) Had you worked?
(Why) Had she slept?

3. The Past Perfect Simple is
used:
S To describe an action
which was completed
before a specific point of
the time in the past.
My mom had done the
dishes by midnight.

4. S To describe an action that
was completed before
another action in the past.
S The movie had already
started when we got to the
movie theater.
NOTE: We use the Past Perfect Simple for the action that happened first
ant the Past Simple for the action which followed.

5. TIME EXPRESSIONS
Before + point in time
By + point in time
Before, After, When, By the time
Already, Ever, Never, Just