The pluperfect tense relates action that is "extra perfect" (plu-, sort of like "plus"); i.e. action that is more than complete. We get the sense of the pluperfect by translating a verb as "I had praised", "I had praised" &c.
To form the pluperfect active indicative, find the perfect stem (the 3rd principle part less the final "i"), and add the personal endings.
Note: the personal endings are the same as the imperfect of sum. (This might help you grasp the "extra" pastness of this tense: the perfect stem is one pastness, and the imperfect of sum is another, an "extra", Â pastness.)
To add: pluperfect active subjunctive, pluperf passive indicative, pluperf passive subjunctive.