Paris Roissy Charles Degaulle airport ( CDG ) to Versailles by the public transport
It will take you around 1 hour and a half from Paris CDG to Versailles and its Palace.
From the airport terminal 1 or terminal 2, the quickest way is to go directly to the center of Paris by train using the RER B and then to change for another train using RER C to get to Chateau de Versailles..
Then look out for the sign RER C and take the direction “ Versailles Rive Gauche chateau de Versailles “. This station is the line terminus. Just make sure that you take the correct direction.
A single ticket CDG to Versailles will cost you around 12€. Double price for a return fare.