Hi Mintoo,

this question has been elaborated on many times already. There are great examples and discussions on this topic on the internet, if you google the question. I suspect these are more helpful than my reposting what has already been said several times. 

Try these for a start:

https://en.m.wikipedia.org/wiki/Passé_simple

https://french.stackexchange.com/questions/9/différence-entre-le-passé-simple-et-le-passé-composé

 

-- Chris.