There are 2 RER B stations in the airport, Aéroport Charles-de-Gaulle 1 which serves terminals 1 and 3, and Aéroport Charles-de-Gaulle 2 located next to terminal 2.
One way ticket to Paris costs 9.50€. You can buy it at the entrance of the RER stations or in any metro ticket office.
It takes approximately 30 minutes to reach Paris from the airport of Roissy-Charles de Gaulle.
4 stations of RER B are located in Paris, Gare du Nord, Châtelet – les Halles, St-Michel – Notre Dame and Denfert Rochereau.