The perfect system (for both the indicative and subjunctive moods) includes the perfect, pluperfect and future perfect tenses in both the active and the passive voice. Each tense has a "pastness" about it: we translate the perfect either using "has" or "have" (I have walked, he has walked), "did" (I did walk), or simply just with "-ed" (I walked). We translate the pluperfect using "had" (I had walked). We translate the future perfect as "will have" (by tomorrow, I will have walked 5 miles).
This system is formed from the 3rd principle part. First you find the perfect stem (the 3rd principle part minus the final "i"), then you add the appropriate endings.