The past continuous and the past simple help us to show how two past actions or situations are connected.
When we use these two tenses together, it shows us that the past simple action happened in the middle of the past continuous action, while it was in progress.
While I was studying, I suddenly felt sleepy.
We often use these tenses to show an action interrupting another action.
I broke my leg when I was skiing.
As I was going to work, I saw an old friend.
We were watching television when the power went off.
Can you see a difference in the meaning of these two sentences?
When the guests arrived, Jane was cooking dinner.
When the guests arrived, Jane cooked dinner.
In the first one, Jane started cooking dinner before the guests arrived. We know that because it uses the past continuous. In the second sentence, the guests arrived first and then Jane started cooking.