The Past Continuous: Meaning

Interrupted continuous actions in the past (used in conjunction with the past simple)

When I arrived, they were serving lunch.

I was sleeping when she called me

The Past Continuous: Forms

Affirmative (Positive)

We got married when we were living in Moscow.

Form: Subject + was/were + verb (ing)

Negative

They weren't waiting at the bus stop.

Form: Subject + was/were + not + verb (ing)

Question (Interrogative) 

Where were you living?

Form: Was/were + subject + verb (ing)?