There are taxis available 24/7 from taxi ranks outside all the airport’s terminals, taking about 40min to the centre of Paris and costing approx. €60. If you want to catch the train, you can head to terminal 3 (you can catch a shuttle if you landed in terminal 1 or 2) where the airport train station can be found. From there, you can buy a one-way ticket into Paris for around €10 per adult. The train (the RER B) leaves every 10-15min.