passe compose is usually reserved for complete past actions
annoucnes what happened, actions that were completed
* je suis arrive tot (i arrived early)
* j’ai fini mes devoirs (i finished my homework)
passe compose expresses what happened a specific number of times
* j’ai etudie lundi (I studied on (a specific) Monday)
* j’ai perdu mon livre deux fois (i lost my book twice)
passe compose reports a change in a state of being, a new feeling
* a ce moment, j’ai deteste l’ecole (at that moment, i hated school)
* j’ai ete inspire par ton succes (i was (became) inspired by your success
passe compose interrupts an imparfait verb with news of some occurance
* j’etais a l’ecoloe quand il a commence a pleuvoir (i was at school when it started raining)
* j’essayais d’etudier mais mon ami m’a pose une question (i was trying to study but my friend asked me a question)