The French word imparfait is the imperfect English tense, and passe compose present perfect tense in English. Imparfait speaks to past situations, and passe compose speaks of specific circumstances. More to the point, imparfait can set the stage for a situation expressed with passe compose.
Imparfait can also lay the groundwork for a condition expressed with passe compose. Imparfait is used for ongoing action. Passe compose used for some events that started and ended in the past time. Imparfait is also used for repeated or habitual actions.