We use the Past Continuous to describe a continuing action in the past:
He was playing tennis.
She was talking to her friends.
Use a past form of be + -ing to form the Past Continuous:
What were you doing?
Was David having breakfast?
Sorry, I wasn’t listening to you!
We often use the Past Continuous to set the scene, begin a story, introduce an anecdote, etc.:
He was playing tennis when the phone rang.
She was talking to friend. Suddenly, they heard a noise.
I was getting my dinner. Then, the lights went out.