had + p.p.
RuleSubject + had + past participle: an action completed before another past action or time (the past before the past).
Curiosity
When two things both happened in the past, how do you show which one came first?
Intuition
The past perfect steps one further back. "had + p.p." is the earlier past; the simple past is the later past — like a flashback.
Visualization
See it on the timeline: two points inside the past. The first-finished event (had + p.p.) sits further left, the later event to its right, then now.
had + p.p. marks the earlier of two past events.
NOW
the meeting had ended
earlier past
Essence
Often used with before, after, by the time, when. A typical frame: "By the time + simple past, subject + had + p.p." Mark the first-completed event with had + p.p.
Examples
By the time we arrived, the meeting had ended.
He had never used the software before he joined us.
She realized that she had forgotten the password.
Mini-quiz
"By the time the manager arrived, the staff ___ the setup." Which fits?