what are the differences between past perfect and past progressive

past perfect is like the past of the past, you usually use it when you tell a story about smth thats happened in the past and u wanna point out that smth happened before smth else
u use past progressing when u talk about an action thats happened in the past and is continuous

examples:
he told me that he had alr seen this movie - he saw the movie before telling me about it
i was showering when he returned home - returning home is an immediate action while showering is a long continuous action

u can think of past perfect as the past form of present simple and of past progressive as the past form of present progressive

hope its clear and if not u can lmk :)