The Past Continuous tense expresses action at a particular moment
in the past. The action started before that moment but has not finished
at that moment. For example, yesterday I watched a film on TV. The film
started at 7pm and finished at 9pm.
At 8pm yesterday, I was watching TV.
past
present
future
8pm
At 8pm, I was in the middle of watching TV.
When we use the Past Continuous tense, our listener usually knows or
understands what time we are talking about. Look at these examples:
I was working at 10pm last night.
They were not playing football at 9am this morning.
We often use the Past Continuous tense to "set the scene" in stories.
We use it to describe the background situation at the moment when the
action begins. Often, the story starts with the Past Continuous tense
and then moves into the Past Simple tense. Here is an example:
"James Bond was driving through town. It was raining. The wind was blowing hard. Nobody was walking in the streets. Suddenly, Bond saw the killer in a telephone box..."
Past Continuous + Past Simple
We often use the Past Continuous tense with the Past Simple tense. We use the Past Continuous to express a long action. And we use the Past Simple to express a short action that happens in the middle of the long action. We can join the two ideas with when or while.
In the following example, we have two actions:
long action (watching TV), expressed with Past Continuous
short action (telephoned), expressed with Past Simple
past
present
future
long action: I was watching TV from 7pm to 9pm.
8pm
short action:
You phoned at 8pm.
We can join these two actions with when:
I was watching TV when you telephoned.
Notice that "when you telephoned" is also a way of defining the time (8pm).
We use:
when + short action (Past Simple)
while + long action (Past Continuous)
There are four basic combinations:
I was walking past the car
when
it exploded.
When
the car exploded
I was walking past it.
The car exploded
while
I was walking past it.
While
I was walking past the car
it exploded.
Notice that the long action and short action are relative.
"Watching TV" took two hours. "Telephoned" took a few seconds.
"Walking past the car" took a few seconds. "Exploded" took milliseconds.
Information taken from: https://www.englishclub.com/grammar/verb-tenses_past-continuous_u.htm
