Past simple—Indicates a finished action. Something that happened in the past which has no connection to the moment of speaking.
Past continuous—An action that happens in the past and is interrupted by another action. This verb can never stand alone, it must have a complement verb.
Past perfect—Usually used when there is more than one action happening in the past in a certain order.
Usage of Past Simple:
I lived in Paris.
(In the past, I lived in Paris.)
I taught English.
(In the past, I taught English.)
I ate lobster.
(In the past, I ate lobster.)
Usage of past continuous:
I was living in Paris when France won the World Cup.
(During my action of “living in Paris," France won the World Cup.)
I was teaching English when the student got sick.
(While I was in the middle of teaching, the student got sick.)
I was eating lobster when the phone rang.
(While I was eating, the phone rang.)
Usage of past perfect:
I had lived in Paris before I went to school in England.
(First I lived in Paris, then I went to England.)
I had taught English before I finished my degree.
(Teaching came before finishing my degree.)
He said he had eaten too much lobster.
(In the past, the man said that he performed the action of eating.)