There are four main tenses that can be used to describe past events.
SIMPLE PAST
It is used to talk about a situation that happened and finished in the past, a completed action. We usually say or know when the action happened. The moment in the past is clearly defined.
PAST CONTINUOUS
It is used to talk about something that started before a certain time in the past and was still in progress at that time.
We usually use it to describe a situation, to give the background to a scene that happened in the past.
We use it to describe that a situation that was in progress was interrupted.
PAST PERFECT
It is used to talk about an earlier past, when something happened in the past before another thing, we use the past perfect for the first action (late past).
PAST PERFECT CONTINUOUS
It is used if we want to emphasize that something had been in progress continuously up to a certain time in the past.