TGV - 100% Prem's

Which website are you looking at, and for what date?

I don't know about the 100%, but Prems is short for premiers, the first and cheapest tickets available for a route. Yes, anyone can buy these tickets, as long as you do before they sell out (quickly on peak routes at peak times). These tickets will be non-refundable and non-exchangeable - for any reason - so be sure of your plans before booking. If you book early enough, you can often get first class for just a few more euros than second class.

To buy French train tickets, you can use the official SNCF website https://en.voyages-sncf.com/en/, if it will take your credit card or Paypal. Be sure to stay on that site and refuse to be redirected to Rail Europe. If you can't get SNCF to work, try Trainline (formerly Captain Train) https://www.trainline.eu/, which by all accounts is easy to use with US credit cards and offers the same prices as SNCF.

Ryan,
Harord has given you excellent advice.
My daughter & I took this train, but in reverse, Annecy to Avignon Centre & also purchased the discounted tickets you're referring to. As far as I know, there's no direct train traveling this route, but you can choose the train route that requires one change, instead of two. If you'll chose this route, you'll transfer to a TGV train at Valence Ville.
Make sure you take a picnic lunch or a snack, as it's a long trek, but the scenery is nice and the train ride is comfortable.

Here is the explanation on 100% Prem tickets, from the SNCF.com website:

100% Prem’s fare means discounted 1st and 2nd Class TGV tickets.

It is available for some trains (France only) with all seats at Prem’s
fares (the lowest prices), especially the first trains in the morning
and trains at night during the following periods:

Weekends: between Thursday lunchtime and Sunday evening During school
holidays: on off-peak train services

These tickets cannot be refunded or exchanged. If you took out
insurance when placing your order and are unable to travel, you must
cancel your tickets on our website and send your claim for
reimbursement to the insurance company.

Annecy is a gem, our favorite place in France! :-)

Hopefully you'll experience one of their market days, they're superb!
We arrived on a Saturday, and enjoyed browsing through their antiques street market, then on Sunday we had our fill at the farmer's market...And... On Tuesday, there was another market!

Make sure you try the ice cream at Glacier des Alpes, it's creamy & delicious!
If you need suggestions as to where to eat a nice meal, without breaking the bank, send me a PM.

Have a wonderful trip!

P.S. Edit to add...
I forgot to give you this very informative website about train travel in France (and elsewhere) The man in seat 61

Thanks Harold and Priscilla. This helps a lot.