Hello, I googled that there is train from Charles de Gaulle airport to reach Paris downtown. The train called TGA. Is this train part of Paris metro system or this is completely different? Do you suggest to book it in advance or buy a ticket when I land? Thank you in advance.
The train from CDG to Paris is the RER B not the TGA. I don't even know what TGA is unless you have a typo and mean TGV. In that case, TGV is the high-speed French train line and while it does have a station at CDG, the trains that leave from there are high-speed trains travel to cities other than Paris. Now back to getting to Paris from CDG, the RER B is a suburban train system that connects Paris with its suburbs. It is not part of the metro system but is not completely different in that you can make connections to the metro system at certain stops in the city and the RER trains all have multiple stops, most with connected metro stations, within the city itself. From CDG to Paris, you would have to purchase a ticket that costs around 11€ for a single ride ticket and you would transfer at one of the stations in the city that the RER B stops at to get to the metro and continue to travel on that ticket to your destination. Loads of information on the metro and RER systems is available at parisbytrain.com. As a suburban commuter train, there is no "booking" tickets for the RER. I have never bought RER tickets in advance and I do not know if one can.
And , by studying this , you will have all your answers , presented in a cogent narrative - https://parisbytrain.com/
simultaneous posts , arriving at the same conclusion
As well as Paris By Train, this official site provides interactive planning, fares etc: https://www.ratp.fr/en
Paris is zoned so CdG is several zones away from the centre. Buy a ticket for the amount to your hotel destination. It will allow you to transfer from the RER regional train to the Metro. Hold on to the ticket; you need it to exit the RER and enter the Metro. Never discard the ticket until your journey is finished and you are outside the destination station. There are spot checks to make sure you have a valid ticket and the fines are stiff. (PS: You exit the Metro by simply pushing open a gate.)
Some visitors worry about buying a transit pass. I just get a "carnet" -- a package of 10 single tickets good for the central area of the city. They work on buses and surface light rail too but without transfer. The links above will explain the rates.
Thank you everyone!