Past perfect

The past perfect is formed by combining the auxiliary verb "had" with the past participle.

I had studied.
He had written a letter to María.
We had been stranded for six days.

Because the past perfect is a compound tense, two verbs are required: the main verb and the auxiliary verb.

I had studied.
(main verb: studied ; auxiliary verb: had)

He had written a letter to María.
(main verb: written ; auxiliary verb: had)

We had been stranded for six days.
(main verb: been ; auxiliary verb: had)

In Spanish, the past perfect tense is formed by using theimperfect tense of the auxiliary verb "haber" with the past participle. Haber is conjugated as follows:

había
habías
había
habíamos
habíais
habían