for two or more actions which were happening at the same time in the past(simultaneous action).
he was walking down the street when he saw his friend tom.
I was reading a book while my brother was listening to music.
to give background information in a story.
the sun was shining and the birds were singing Peter woke up...
time expressions used with the past continuous: while,when,as,all day/night/morning,all day yesterday,etc.
for an action which happened at a stated time in the past.
he got married last Saturday.
for actions which happened one after the other in the past.
first he rang the door bell and then he opened the door.
for an action which was in progress at a stated time in the past.
At 10 o'clock yesterday morning,the gardener was watering the plants.
for two or more actions which were happening at the same time in the past(simultaneous actions).
she was watching TV while her husband was reading the newspaper.
to show that someone was interrupted in the middle of an action that interrupted it.
/was watching TV when the phone rang.