The perfect tense relates past, completed action. It differs from the imperfect in that the imperfect relates ongoing, repeated, or continuous action. For this reason, the perfect is translated as "I have praised", "I did praise, or simply "I praised".
To form the perfect active indicative, find the perfect stem (the 3rd principle part less the final "i"), and then add on the personal endings for the perfect:
To form the perfect active subjunctive, find the perfect stem, add "-eri-" then add the regular personal endings.
To add: perfect passive indicative, and perfect passive subjunctive