Use

Use of the Past Perfect Tense

to express a past action that took place before a past moment or before another action in the past. In fact it is the past equivalent of the Present Perfect. Note the use of when, before, now that, as soon as, and after in some of the sentences contaioning a Past Perfect.
to express duration up to a certain moment in the past.
with just, already, hardly/ barely/ scarcely and no sooner, to show that the past action was finished a little time before another past action.
with since and for when the point of reference is past.
in Indirect Speech, to express a Past Tense or a Present Perfect from Direct Speech.
to express a Past Conditional in a conditional clause.
to express an unfulfilled wish.
after had/ would rather( when the subjects are different) or as if/ as though.
to express a future action that takes place before another another action expressed by a Future-in the -Past.
with such verbs as: to expect, to hope, to intend, to mean, to think to express past hope, intention which was not fulfilled.