Thank you for using the Jiskha Homework Help Forum. This is a lesson I always loved to do! Let's see if we can't clarify it for you.
In ONE word, l'imparfait is DESCRIPTION, while the passé composé is ACTION.
Uses of the passé composé: is used to denote action completed. It had a beginning, a middle and an ending. The English cues are "DID" or "-ed". For example, il a marché dans la rue. = He walkED, he DID walk in the street. This action is over and done with.
Uses of l'imparfai: is used to denote continuous and repeated action. Thus, the signs of this tense in English are "WAS + ING", "used to...." For example, il marchait dans la rue. = He WAS walkING, he USED TO walk in the street. As far as we know he is still walking, because there is no ending that you know of. We are concentrating on the "middle" of that action. When it comes to time and age, it's l'imparfait unless someone waved a magic wand and POOF suddenly time or age changed!
The problem comes from the English when we say "He read the book." Now you have to decide if he DID read that book (passé composé) or WAS readING, USED TO read that book (l'imparfait.)
After a while you will get a "feeling" for the difference. The passé composé is like snapping a photo, while l'imparfait is like shooting a movie. Imagine these images: / / / / / = passé composé, one action, followed by another versus ~~~~~~~~ = l'imparfait.
You will also notice certain word cues for each tense. Last night, one day, yesterday = passé composé versus every day, always, while... = l'imparfait.
The best thing to do is analyze exercises where you must decide which past tense to use. Please feel free to ask any questions.
do you have any websites that provide this kind of exercises?