In general, we use imparfait to talk about our memories from the past. Imparfait indicates actions that were continuous, not momentary. For example: "Quand j'avais les boucles d'oreilles, j'aimais les porter." (When I had earrings, I liked to wear them.) or Il faisait froid. J'attendais le bus. (It was cold. I was waiting for the bus.)In contrast, passé composé represents movement, a change in a course of actions. If I continue my story about earrings, I could say "Il y a deux ans, je les ai perdu." (Two years ago, I lost them.) or "Le vent a cassé mon parapluie quand j'attendais le bus." (The wind broke my umbrella, when I was waiting for the bus.) Moreover, passé composé goes with specific time period, which is well-defined: "de 1669 à 1723" (from 1669 to 1723); "entre XIIe et XIVe siècle" (between the 12th and 14th centuries).