The PAST PERFECT tense in English is very useful because it helps you to improve your level given that you practice the past participle of regular and irregular verbs, but you need a lot of practice!
After that, your English will sound much better!
Thanks to perfectenglishgrammar.com we have an interesing explanation that includes the details of the use of this tense in English and some practice.
Exercise 1: affirmative and negative
Exercise 2: interrogative
