Past Perfect Tense

The past perfect is used to clarify the order of two past actions the past perfect and the second uses the simple past . 

This is the rule of the past perfect :

subject + had + past participle of the main verb

Affirmative form

I had worked

You had worked

He/She/It had worked

We had worked

You had worked

They had worked

Negative form

I had not (hadn't)  worked

You had not worked

He/She/It had not worked 

We had not worked 

You had not worked

They had not worked

Interrogative form

had I worked ...?

had you worked ...?

had he/she/it worked ...?

had we  worked ...?

had you worked ...?

had they worked ...?

Example :

They had finished their homework when I called them .

Before he entered , he had shut the door .

They had gone for the trip when you reached them .