Imperfect and Passe Composee is what I hope you're talking about. Imperfect is good for recurring actions and actions that do not have a defined beginning and end. passe is good for defined actions that have times or you kbow when it ended, like closing a door. once it's shut, it's shut. however, in sentences with an interrupted and interrupting action, the action that interrupts is Passe and the interrupted is imperfect. hope this helps!
