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

The past participle does not change forms when it is used in the preterite perfect tense.  For example, nosotros hubimos visto, ustedes hubieron visto, ella hubo visto, etc.  For speakers of modern Peninsular and Latin Americn Spanish, the preterite perfect is a literary tense.  While it is no longer spoken, it is fairly common to run across the preterite perfect when reading.  If you see this tense in print, be aware that it has the same meaning as the pluperfect:  Yo hube escrito la carta para cuando él me la solicitó  (I had already written the letter when he asked me for it).