What is the difference between the passé composé and imparfait?

The passé composé is used to express a completed action in the past, whereas the imparfait can be used to describe an ongoing state or action, or something that used to happen.Passé composécomplete actionJ’ai fini mes devoirs.(I finished my homework)countedJ’ai perdu mon livre deux fois.(I lost my book twice)newÀ ce moment, j’ai détesté l’école.(At that moment, I hated school)Imparfaitincomplete actionJe faisais mes devoirs.(I was doing my homework)uncountedJe perdais constamment mon livre.(I always used to lose my book)ongoing/continuousJ’aimais l’école.(I liked school)Here's a sentence that uses both tenses...Je faisais mes devoirs quand le téléphone a sonné.(I was doing my homework when the phone rang)