TGV Paris to Avignon

Have you done any checking at all? Have to tried rome2rio.com? SNCF? When are you going? How far in advance? Probably if you indicate you've done all these things and still somehow, someway still have an issue, community might be able to help.

I like Trainline.

https://www.thetrainline.com/en-us

Here's the official site of SNCF, the French rail system. And here's a lot of info about rail travel in France, particularly from Paris. You have multiple choices. Generally fares will be lower the earlier you book, just like airlines. There are multiple daily trains, taking roughly 2.5-3.5 hours depending on which one. Avignon has a central station and a separate TGV station not far outside the city, with shuttle service into the city. I think the fastest way to do this is to the TGV station, but I haven't done myself. Trains depart from Paris' Gare de Lyon.

If you are unfamiliar with European trains and train companies, I would suggest reading through the Man in Seat 61 website. https://www.seat61.com/

It should help you familiarize yourself with the process. Buy your tickets directly from the train company operating the train whenever possible. For France, that would be SNCF. Their website will show which trains are travelling on the day, time of travel, any changes required, and price.

If for some reason you are unable to use the official site, and choose to go with a 3rd party reseller, then trainline has a decent reputation. But they may not show all options, and will charge an extra fee.

lellerbrook5,
Last year I booked more than one train trip on the SNCF website. After a bit of exploring the site, I was able to figure out how to use it and book TGV tickets from Bordeaux to Paris (Gare Montparnasse). We also took the TGV from Paris (Gare de Lyon) to Marseille. This is the same line that will take you to Avignon. If you go on the website and put in Paris to Avignon, you should be automatically "assigned" to Gare de Lyon, the station where trains to the south leave from. We have taken slower local trains as well, but the TGV service is great. We picked our reserved seats and because we bought them early enough in advance, we chose first class (not much more in price) because there was a little more space for our luggage (behind our seats). We were four so chose seats facing each other with a table between them. Someone came around and took our order for some food and drinks. There was time for that on the Paris-Marseille trip. Familiarize yourself with the site and it isn't too complicated. I spent about half an hour playing around with it to get comfortable, and I am 80 years old, not quick on the computer (I just recently learned how to cut and paste!), and conquered the dreaded SNCF site!
Oh yes, if you see a good price for the journey you are sure you want, jumnp on it! I hesitated one time and it cost me about 20 euros more per ticket.
Bonne chance!

I have used both Trainline and the SNCF app to book trains in France. I find the SNCF app provides a little more information on the specifics of the train journey, and it is also better if you are planning on reserving seats in that you can view all available seats. I used the app to purchase and store my tickets on as recently as this month, and it worked fine. Fast trains from Paris Gare de Lyon to Avignon TGV take between about 2:40 and 3:20. Be aware that there is also a TGV station at CDG airport with fast trains running directly to Avignon without going through Paris, which take just about the same amount of time.