different usage of the simple past and the past perfect in the practical application:
the simple past
The simple past relates to an action in the past in a certain point in time in the past, and
has no connection to the present.
The past perfect is used in the English, when an action in the past is over, before another one starts.(anteriority).
The past perfect is almost never used on its own, but mostly in connection with the simple past.
for example: When we arrived at the stadium, the game had already started.