What is the difference between the perfect tense and the imperfect tense?

Both tenses are used to describe something that happened in the past. In every day conversation, the perfect tense is almost always used e.g. j'ai joué, j'ai trouvé.... When writing, the perfect tense is used to describe something that happened once. E.g. La semaine dernière j'ai visité ma mère en France. The imperfect is used to describe something that happened repeatedly, or regularly in the past. For example, quand j'étais petite, je visitais mes grand-parents chaque week-end. (When I was little, I used to visit my grandparents every weekend). The imperfect is also used to describe something that went on for a sustained period in the past, for example ..