There are two train stations in Avignon:
- Avignon Centre is the one near the city center
- Avignon TGV is on the outskirts of town and is from where most of the long distance trains depart
There are regular trains (about every half hour) between Avignon Centre and Avignon TGV.
You can purchase a ticket to Frankfurt on SNCF Connect. I’d suggest that you download the app. Make sure you spell Frankfurt correctly (with a ”u” rather than an ”o”). The main train station in Frankfurt is Frankfurt Haubtbahnhof (Hbf). Make sure you know the Avignon station from which your train departs.
I would suggest trying SNCF Connect first when you buy tickets. This will give you a price with no additional fees. I used it recently with no issues. However, if you run into problems you can try Trainline. Trainline is a reseller with an easy to use interface; they charge an additional fee if you buy through them.