Yesterday -
How to use the Past Continuous with the Simple past:
Past Continuous + when + Simple Past
OR
Simple Past + while + Past Continuous
Observe:
4.30 pm

Ann's father came back home. (a quick action)
|
4 o'clock to 5 o'clock

Ann was reading the book. (For one hour)
|
Compare:
Ann was reading the book when her father came home.
OR
Ann's father came home while she was reading the book.
Examples:
1. Pete rang while I was watching TV.
2. Jane was playing tennis when it started to rain.
3. Jack was walking home when the dog attacked him.
4. I fell down and broke my leg while I was skiing.