The positive - make it with 'had' + the past participle (usually made by adding 'ed' to the infinitive, but a few verbs have irregular past participles)
The short form for 'had' is 'd.
- I had been (I'd been)
- You had gone (you'd gone)
- She had met (she'd met)
(Be careful not to confuse it with 'would'. Would is followed by the infinitive - 'I'd go', whereas had is followed by the past participle - 'I'd gone').
For the negative just add 'not':
- I had not been (I hadn't been)
- And to make a 'yes / no' question put 'had' before the subject:
- Had I come?
- Had you eaten?
- Had she gone?
For 'wh' questions put the question word at the beginning: - When had I come?
- Why had you eaten?
- Where had she gone?
- When had it rained?
- How had we met?
Finally here's an exercise about past perfect questions. Go to: http://www.montsemorales.com/gramatica/PastPerfect1.htm