When do I use the passe simple and when do I use the imparfait?

When deciding what verb tense to use between the passe simple and the passe compose, you need to think about the type of action that is being performed. Say you are telling a story about the past. To set the scene and describe something that lasts in time you use the imparfait. (For example: During our childhood we used to spend Christmas with our grandparents. Pendant notre enfance, nous passions Noel avec nos Grandparents. )Generally descriptions are made in the imperfect.For an action that is sudden and will only last for a brief period in time, we use the passe simple. (Example: The policeman jumped onto the thief, Le policier sauta sur le voleur)When writing a story in the past tense these two tense are the most used, and must be used together.