Past simple./past continous.

We use past simple when we speak about things that happened any time before the moment of talking, when it’s a finished action in a finished time.

Structure:
- Affirmative: Subject + Verb finished in ED / past simple of irregular verb.
Example à I listened to music yesterday. / I came back last Friday.
- Negative: Subject + verb auxiliary “do” in the past-negative form DIDN’T.
Example à I didn’t listen to music yesterday. / I didn’t come back last Friday.
When in the sentence is “didn’t or did” the verb must be in present, because did/didn’t express the past at all.
- Interrogative: verb auxiliary “do” in the past tense DID + subject + verb in present + ?
Example à Did I listen to music yesterday? / Did I come back last Friday?


We use past continous when we speak about things that were happening in the past. The past continous is an action in progress in the past.

Structure:
- Affirmative: Subject + was/were + verb finished in ING.
Example -- I was reading a book / they were playing in the garden.
-Negative: Subject + wasn’t/weren’t + verb finished in ING.
Example -- I wasn’t reading a book / they weren’t playing in the garden.
-Interrogative: Was/were + subject + verb finished in ING. + ?
Example -- Was I reading a book? / Were they playing in the garden?

Credits: http://www.aulafacil.com/Ingejerc/Lecciones/Lecc19.htm