Compare the past continuous (I was doing) and past simple (I did):

Past continuous (in the middle of an action)

Past simple (complete action)

  • I was walking home when I met Helen. (= in the middle of walking home)
I was walking home when I met Helen. - English Grammar - Past Continuous and Past Simple
I was walking home when I met Helen.

 

  • I walked home after the party yesterday afternoon. (= all the way, completely)
I walked home after the party yesterday afternoon. - English Grammar - Past Continuous and Past Simple
I walked home after the party yesterday afternoon.

 

  • Sarah and Carol were watching television when the phone rang.
Sarah and Carol were watching television when the phone rang. - English Grammar - Past Continuous and Past Simple
Sarah and Carol were watching television when the phone rang.

 

  • Sharon watched television a lot when she was ill last year.
Sharon watched television a lot when she was ill last year. - English Grammar - Past Continuous and Past Simple
Sharon watched television a lot when she was ill last year.

 

We often use the past simple and the past continuous together to say that something happened in the middle of something else:

  • Tony burnt his hand when he was cooking the dinner.
Tony burnt his hand when he was cooking the dinner. - English Grammar - Past Continuous and Past Simple
Tony burnt his hand when he was cooking the dinner.

 

  • I saw you in the park yesterday. You were sitting on the grass and reading a book.
I saw you in the park yesterday. You were sitting on the grass and reading a book. - English Grammar - Past Continuous and Past Simple
I saw you in the park yesterday. You were sitting on the grass and reading a book.

 

  • While I was working in the garden, I hurt my back.
While I was working in the garden, I hurt my back. - English Grammar - Past Continuous and Past Simple
While I was working in the garden, I hurt my back.

 

But we use the past simple to say that one thing happened after another:

  • I was walking along the road when I saw Lisa. So I stopped and we had a chat.
I was walking along the road when I saw Lisa. So I stopped and we had a chat. - English Grammar - Past Continuous and Past Simple
I was walking along the road when I saw Lisa. So I stopped and we had a chat.

 

Compare:

  • When Jason arrived, we were having dinner. (= We had already started dinner before Jason arrived.)
When Jason arrived, we were having dinner. - English Grammar - Past Continuous and Past Simple
When Jason arrived, we were having dinner.

 

  • When Jason arrived, we had dinner. (= First Jason arrived and then we had dinner.)
When Jason arrived, we had dinner. - English Grammar - Past Continuous and Past Simple
When Jason arrived, we had dinner.

 

There are some verbs (for example, know/want/believe) that are not normally used in the continuous:

  • We were good friends. We knew each other well. (not “we were knowing”)
We were good friends. We knew each other well. - English Grammar - Past Continuous and Past Simple
We were good friends. We knew each other well.

 

  • I was enjoying the party but Mary wanted to go home. (not “was wanting”)
I was enjoying the party but Mary wanted to go home. - English Grammar - Past Continuous and Past Simple
I was enjoying the party but Mary wanted to go home.