The pluperfect tense is constructed by using the imperfect form of the irregular verb haber with a past participle:
 

The past participle does not change forms when it is used in the pluperfect tense.  For example, él había hablado, yo había hablado, tú habías hablado, etc.  Like its English counterpart, the pluperfect tense is used to refer to an action completed further back in the past than some other action; it puts past events into a time sequence: Yo ya había cocinado la cena cuando mis amigos llegaron  (I had already cooked dinner when my friends arrived).