Past continuous.

Form: was/ were + -ing

Use: 1.To describe an action which was in progress at a definite time in the past.

eg. I was playing football at nine o'clock last night.

2. To describe a lengthuous action in the past which was interupted by a short one.

eg. I was having a shower when the phone rang.

3. To describe two parallel actions in the past.

eg. I was cooking while my sister was tidying her room.