Introduction:

Use the past perfect to express the past of the past.
Remember that it functions also as all perfect tenses. So you use it with 'since, for, yet, already'. It is an action before another action in the past.

Structure:

Subject + had + verb / Had + subject + verb? / Subject + had not (hadn't) / Hadn't + subject + verb / Had + subject + not + verb
Remember that the past perfect is also used in the third conditional (grammar lesson 33).
If I had seen him I would have talked about it.

Examples:

I had been there. / I'd been there.
Had I been there?
I hadn't been there. / I'd not been there. / I had not been there.
Hadn’t I been there?
They had not seen him. They'd not seen him.
Before the school reunion I had not seen Jack for 10 years.
Before our meeting last week, I had not seen the contract yet.