The pretérito pluscuamperfecto is formed by the auxiliar verb "haber" in the imperfect tense followed by the past participle of the main verb. It is the equivalent of the past perfect in English, formed by the auxiliar verb "to have" in the past tense followed by the past participle of the main verb.
Yo había estudiado mucho para el examen. I had studied a lot for the exam.
Cuando la policía llegó al banco, los ladrones ya se habían escapado por la puerta trasera. When the police got to the bank, the thieves had already escaped through the back door.
The pretérito pluscuamperfecto conjugation for regular verbs is: