The past continuous tense is used when the subject of the sentence was previously in the process of doing something, which was then interrupted.

For example:

• Lucy was singing when the phone rang
• Emma was shopping when it began to rain
• I was skiing when I fell and broke my leg.

You can see more examples in our English past continuous video lesson online. This video is part of our package of lessons that enables ESO students study English grammar online, in their own time, at their own pace. Our media package includes video lessons about English grammar and audio recordings to improve listening, vocabulary and pronunciation.