This is a common issue for learners of French. A thorough answer would need a book chapter. Here are some suggestions:

1. https://about-france.com/french/past-tenses.htm
2. https://www.lawlessfrench.com/grammar/verb-timeline/
3. https://www.thoughtco.com/different-past-tenses-in-french-1368902
4. https://www.cliffsnotes.com/study-guides/french/french-ii/french-ii-past-tenses/using-the-correct-form-of-the-past-tense

Judging from your profile I guess you are Greek. I suggest you look at:

1. http://brixfax.co/mf/grammaire/verbes/les-temps/
2. https://www.scribd.com/document/365720056/Χρόνοι-στα-γαλλικά

See also the different links inside the suggested web pages. Speaking very briefly you just need be able to recognize passé simple. It is not used orally (at least in colloquial French). Use passé composé instead.

Plus-que-parfait is like past perfect in English or Ypersyntelikos in Greek language. Hence a typical example would be

Quand je suis arrivé(e), il avait déjà mangé.

In this way plus-que-parfait expresses what is called “antériorité dans le passé”.

http://revuescolaire.over-blog.com/2017/02/le-temps-ii-l-anteriorite/la-posteriorite.html

Another typical example:

Si j’avais su, j’y serais allé(e).

which can be translated in English as:

Had I known, I would have gone there.

See below for more examples and exercises:

https://www.francaisfacile.com/exercices/exercice-francais-2/exercice-francais-47893.php

• Passé simple = I did (je fis)
• Plus que parfait = I had done (j’avais fait)
• Passe composé = I have done (j’ai fait)
• Imparfait = I was doing (je faisais)
• Passé antérieur = I had done (j’eus fait)