One of the most difficult decisions a beginner French learner has to make when talking in the past tense is whether to use the simple past tense or the imperfect past tense. To review the passé composé, see A2.1 Modules 3 and 4. To review l’imparfait, see A2.2 Module 2. Review the chart below to read about the different contexts that the passé composé and l’imparfait tenses are used.
Chart from: Cliff Notes
The passé composé is used to express an action that happens at a specific moment. This action/moment has an implied beginning and ending. For example, the sentence provided (Je suis sortie → I went out) implies that at some point, the subject/speaker returned from going out.
The imperfect tense is used to express an action that was taking place over a period of time, with no indication of the action stopping. This can include actions that are simply repetitive or descriptive. In the example sentence, it is implying that the subject/speaker was talking fast over a period of time. If that sentence was put into the passé composé (Il a parlé vite → He talked quickly), then it is implied that at some point, the speaker stopped talking quickly altogether or changed pace.
The distinction between the two tenses is very tricky, especially for beginner learners. Do not be discouraged! If you mistake one tense for the other, a native speaker will still understand your sentence and be able to communicate with you.
Key indicator words can be helpful in identifying which tense to use in your sentence. See the Reading link of this Module to study these French clue words.