Just as the Present Progressive is used for things in progress in the present, the Past Progressive tense is used for things in progress in the past.

Visually, the Past Progressive would be represented like this:

Form:
There are two parts to the Past Progressive:
Be in the past and a present participle (verb ending in -ing.)
I was doing, She was having, We were working and They were playing.

In the Past Progressive, contractions are never used.

Uses:

1. For interrupted past activities. The interruption is usually a verb used in the Simple Past tense after when. The Past Progressive is used with another time or event.

I was driving home when I had an accident.
Were you talking on the phone when you had the accident?
No, I wasn't talking on the phone when the other guy hit me.

2. For things in progress at a specific past time, usually using at.

At 4:00 A.M., I was sleeping.
What were you doing at 6:30? I was having breakfast.

If the time reference is understood, it is not necessary to repeat at ---- .

3. For things in progress simultaneously, usually using while or as

Were you talking on the phone while you were driving?
No, I was trying to find something in the glove compartment as I was driving.

4. For a story describing many things happening simultaneously at a past time.
When I awoke, the sun was coming up. The birds were chirping and the city was coming to life. A few people were driving along the street. It was a beautiful day.