Past perfect in English is the tense that says that someone "had done" something. In Spanish, the conjugation for haber here is the imperfect tense of haber, which will make more sense once we go over imperfect, so hang tight. Below are the conjugations of the verb for past perfect. In imperfect and subjunctive, the first and third person singular conjugations will be the same:
Yo: había
Tú: habías
Él, ella, ud.: había
Nosotros: habíamos
Vosotros: habíais
Uds., ellos/ellas: habían
Some examples:
Yo había leido este libro antes. ｜I had read this book before.
Habías comido. ｜You had eaten.
Habíamos dicho. ｜We had spoken.
Ella había sonreído. ｜She had smiled.
Ellos habían bailado. ｜They had danced.