We don't have past perfect in our language. We express that something had been done before stated time in the past by using a perfective aspect of the verb examples: By six o'clock on Sunday I had already learned all the words = К шести часам в воскресенье я УЖЕ ВЫУЧИЛ(что сделал-perfective aspect) все слова. When we came to the station the train had already gone= Когда мы приехали на станцию, поезд УЖЕ УШЕЛ(что сделал? - perfective aspect)

To correct the Valya's answer Perfective aspect is a requirement, but the main part is use of УЖЕ or similar word

No endings or suffixes are added to verbs in Russian for English Past Perfect case. Gramatically there is only one Past Tense in Russian. We say "I met here 10 years ago" but "I had met her before I went to study" in English, but in Russian the verb doesn't change its form in these examples: "Я познакомился с ней 10 лет назад", "Я познакомился с ней до того, как пошел учиться".