You can easily identify Perfect verbs: they always express the finished action.
How to form Past Perfect Tense?
If you have a look at the table of verbs forms, you'll see, that the formula of Past Perfect is
had V3, it consists of the auxiliary verb had ( to have in its past form) and past participle of the main verb V3.
- good news :1. had is used for all subjects (in singular or plural forms)
I had written ./ He had written./ They had written.
They had painted./ They had not painted./ Had they painted?
When to use Past Perfect?1.for an action which happened before another past action or before a stated time in the past.
He let me use his tablet after he had showed me how to use it.
They had finished the project by Monday.
2. for the action which finished in the past whose result was visible in the past.