|This is a past tense, so it is about something that
|The past perfect is about a past action
that happened before another past action.
|After I had had dinner, I cleared the table.
= First I had dinner, and after dinner I cleared the table
When he had had an accident, they took him to hospital.
= He had an accident, and after the accident they took him to hospital
In a sentence about the past, there are often clues
before, after, when, as soon as, because