I have a conference there :
-how can reach from airport rossy ,cdg or better from paris central by public transport,i have a luggage
-better to stay in paris &go dily for 3days to conference by public transport
-I never visit Chantilly ,is it touristic,we can enjoy staying there
There are public buses from CDG to Maffliers, but it is rather complicated and takes over an hour, so you may be better to get the RER back into Paris Gare du Nord. From there you can get a train to Monsoult-Maffliers which takes around 25 mins. After you have about 1 km walk to the chateau or take a taxi.
for all intents and purposes the bus directions are : In terminal 2B/2D take the bus 351 to Roissypole and alight there (5 mins). From Roissypole take the train no 9518 direction Cergy-Prefecture and get off at Monsoult. There you will still have the walk to the chateau of Maffliers.
Chantilly is well-known for its chateau and its horse-racing and is a very pretty area to visit.
Personally, I'd rent a car so I could do some touring while there, especially to Chantilly with the marvelous Condé Museum which is a must-see in that area. [original link]
If you don't want to rent a car, follow pfsmalo's advice above and take the train to the Gare de Montsoult-Maffliers and then if you have luggage, take a taxi on out to the Chateau. It's not far and won't cost much.
Part of going to a conference is discussing things with colleagues so I'd stay at the conference center. It would also be easier than going back and forth into Paris each day for your meetings. If your meetings are only mornings, then it might make sense since you could do some Paris sightseeing, but if you have morning and afternoon meetings, better have dinner with people you meet there and enjoy the setting. It is a lovely place for a conference so enjoy it.
From Chantilly the train would take you back to Gare du Nord, but this area, although being cheap is not that good. You could take the RER to Chatelet and find something in that area. Most tourists tend to look in the central areas around Notre Dame, the 1st, 2nd, 3rd, 4th, 5th, 6th. These are not the cheapest it would depend on your budget. Personally for a reasonably priced stay which is only a short metro ride away from Gare du Nord is the Bastille area, from where you can easily walk to Notre Dame, the Latin Quarter and you would be on the line no 1 which would take you to the Louvre and further to the Champs Elysées. Much would also depend on your interests, museums, galleries, history or just plain sightseeing.
[original link] when I reach CDg airport usually T2 ,how to proceed after taking our luggage ,to rosy pole how to reach it ,
You will see signs in the halls pointing you to where the buses are.
Hi bus or train to montsoult station
Train from Roissypole, it's all explained in the posts above, read back from the beginning.