Clarification Needed: Does the TGV to Avignon begin at CDG? If so, is its first stop at Gare de Lyon? Or--do I have to go into Paris and catch the TGV train at the Gare de Lyon? This is confusing because some websites imply the former and some the latter. Have looked at both SNCF site and the Suite61. Thanks!
The TGV from CDG to Avignon does not stop in Paris. There are TGVs that leave from Gare de Lyon and others that leave from the airport and no way to take the TGV between Gare de Lyon and CDG. Gare de Lyon is the terminus point for trains heading there and same for CDG.
Trains departing the airport do not stop in Paris; they are not the same trains departing from Paris Gare de Lyon.
If you want to depart from the airport, do your schedule search from Aeroport Charles de Gaulle TGV station, or some variation on that station name, rather than from Paris, for the best shot at the results you want. View details to see any connection points. Results may include both the trains that start from Paris Gare de Lyon (which you can reach by LeBusDirect instead of RER with connections), and those that run directly from the airport. The direct trains take 3h 15m and run a few times per day to Avignon TGV station.
Looking Up Train Schedules and Routes Online gives you the Deutsche Bahn train schedule link and tips for using it. This one doesn't sell tickets; they're available at www.oui.sncf, trainline.eu, and this site. Note that tickets purchased in advance are generally worthless if you miss the scheduled train.
Flexible TGV tickets are available on many routes but they cost substantially more and require dealing with an agent to change the seat reservation. The oui.SNCF site shows the choices. PS: A previous post should have said Seat61, not "suite" and refers to the master of all train schedules and purchases, www.seat61.com
This is a very useful site for showing how to get to the TGV & RER station at the CDG.
https://parisbytrain.com/paris-airport-terminal-2-train-photo-tour/#arrival