I am arriving at Roissy/Charles de Gaulle on Friday, June 21 at 9:30 AM and will be heading to Orleans.
Do I need to buy train tickets in advance?
No you don't need to buy Orleans train tickets in advance of your arrival. You can buy tickets from the TGV ticket office in CDG Terminal 2 train station after you land.
If you feel like booking beforehand, you can do so at https://en.oui.sncf/en/