The PAST PERFECT: The past before the past.

The past perfect grammar structure is as follows:

HAD + past participle

Remember:  Regular verbs have the same past participle as the past tense:
        Ex. walk/walked/walked, talk/talked/talked, create/created/created
                     Irregular verbs have a different past participle than their past tense:
        Ex. go/went/gone, do/did/done, eat/ate/eaten

We use the past perfect to express an action that happened in the past before another action that happened in the past.  Imagine the two events happening in time:

Alice broke up with her boyfriend Christopher.
Alice kissed Mason.

Isn't it important to know which happened first?  Let's imagine both scenarios and the implications using the past perfect:

        Alice had kissed Mason before she broke up with Christopher.  (Alice cheated on her boyfriend.)

        Alice had broken up with her boyfriend Christopher before she kissed Mason.  (Alice did not cheat on her boyfriend.)

The past perfect can clarify the order of events in the past tense.  This is why we use this grammar structure.