What is the difference between the perfect and imperfect tense?

The imperfect tense is used for: Describing actions which are durational or occur over a period of time. For example, “Les Allemands occupaient la France” - this was an ongoing event, and so the use of the imperfect is necessary. It is also used for repeated/continuous actions. If someone performs an action habitually, the imperfect is used. For example, “Quand tu étais en vacances, tu allais au même restaurant tous les soirs”. The imperfect can also be seen as a translation for “I used to do something”. For example: “Je visitais mes grand-parents tous les samedi soirs.”, indicating that this used to happen but no longer does so. It is also used for descriptions of people and physical attributes. For example, “Elle était petite” or “Elle avait des yeux bleus”. The perfect tense (or passé composé) is used for more concrete and finalised actions. For example, “Ils ont acheté une voiture”, as this is one single action which is non-continuous.