“the past of the past”
The following video from Anglo-Link ( click for website) will give you a thorough overview of the formtion and usage of the past continuous, past perfect simple and past perfect continuous(progressive) tenses:
A summary of these tenses as infographics from American English at State:
Here are some quizzes to help you practice these tenses.
Don’t forget to also review other past tenses with my previous lesson: