The Past Progressive Tense

Uses:
1. Something was happening continuously in the past.
It was raining all day yesterday.

2. Something was happening when something else happened.
I was reading when he gave me a ring.

3. Something was happening at the same time as something else was happening.
She was singing as I was talking.

4. Intention in the past with these verbs: going to, planning to, trying to.
I was going to tell you but I forgot it.

5. Reported Speech.
He is looking out of the window.
She said he was looking out of the window.

Special Notes
The Past Progressive Tense is the most usual form in time clauses introduced by as, when and while.