The past continuous describes actions or events in a time before now, which began in the past and was still going on at the time of speaking. In other words, it expresses an unfinished or incomplete action in the past.

It is used:

often, to describe the background in a story written in the past tense, e.g. "The sun was shining and the birds were singing as the elephant came out of the jungle. The other animals were relaxing in the shade of the trees, but the elephant moved very quickly. She was looking for her baby, and she didn't notice the hunter who was watching her through his binoculars. When the shot rang out, she was running towards the river..."

to describe an unfinished action that was interrupted by another event or action: "I was having a beautiful dream when the alarm clock rang."

to express a change of mind: e.g. "I was going to spend the day at the beach but I've decided to go on an excursion instead."

with 'wonder', to make a very polite request: e.g. "I was wondering if you could baby-sit for me tonight."

More examples:

They were waiting for the bus when the accident happened.
Caroline was skiing when she broke her leg.
When we arrived he was having a bath.
When the fire started I was watching television.

How do we make the Past Continuous Tense?

The structure of the past continuous tense is:

subject	+	auxiliary verb BE	+	main verb
		conjugated in simple past tense		present participle
		was were		base + ing

For negative sentences in the past continuous tense, we insert not between the auxiliary verb and main verb. For question sentences, we exchange the subject and auxiliary verb. Look at these example sentences with the past continuous tense:

	subject	auxiliary verb		main verb
+	I	was		watching	TV.
+	You	were		working	hard.
-	He, she, it	was	not	helping	Mary.
-	We	were	not	joking.
?	Were	you		being	silly?
?	Were	they		playing	football?

How do we use the Past Continuous Tense?

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.
What were you doing at 10pm last night?
What were you doing when he arrived?
She was cooking when I telephoned her.
We were having dinner when it started to rain.
Ram went home early because it was snowing.

Past Continuous Tense + Simple Past Tense

We often use the past continuous tense with the simple past tense. We use the past continuous tense to express a long action. And we use the simple past tense 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 tense
short action (telephoned), expressed with simple past tense

past

present

future

Long action.

I was watching TV at 8pm.

	8pm

You telephoned at 8pm.

Short action.

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 (simple past tense)
while + long action (past continuous tense)

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.