I just tried the site
www.sncf.fr. There was a British flag in the top right corner which you could click on to get English. It instantly converts to English and you click on Tickets and Timetables. It then allows you to choose your cities of departure and arrival, dates, times, class etc. and press search. Another form came up asking for the return date to be input again. "Search" again. From this point on it went to a French only site where all the information I had chosen was retained except the return date had once again to be tapped in. Now press "Rechercher". A table comes up with a choice of prices. Presumably you know the days of the week in French. The complication is in understanding the ticket restrictions. Here is a translation:
LOISIR Free exchange and reimbursement up the day before travel, and with a €10 surcharge on the day. After the train has departed no exchange or reimbursement.
NORMAL Exchangeable and reimbursable according to conditions (which are not given here)
PRO 2NDE Exchange and reimbursement free until the departrue, and according to conditions after (again, the conditions aren't given)
PREM'S Not exchangeable or reimbursable
iDTGV Exchangeable before you print it out (it saves you the booking and you can print out just before you go) on paying €10. Not reimbursable.
"Validez cet aller" means choose this outward journey. Then you go through the whole thing again to choose the "retour", the return.
There's an option for insurance that pays you €20 if the train is more than 30 mins late (even though it is their fault!), pays for taxis if you miss a connection because of this, up to €300 for stolen luggage, and transport costs back home if you are taken ill on the holiday (with certain conditions).
"Continuez votre reservation de train" Continue your reservation
"Choisissez comment retirer votre billet" Choose how to get your ticket
"Imprimez votre billet vous même" (for certain tickets only) print your own ticket
"Indiquez votre nom, prenom et addresse electronique" Give us you surname, first name and email address
You then have to tick the box at the bottom to confirm that you agree to their terms and conditions (there is nothing to be afraid of here). "Validez cet etape" Confirm this stage.
Then you select the card you want to pay with, input the details, "Confirmer et payer votre commande" Confirm and pay.
I won't go any further or I will be obliged to buy a ticket! But the only other thing to know is "Poser un simple option à confirmer ultérieurement" which is the chance to give yourself a certain number of days' grace before confirming the reservation and paying. If you don't pay by the date you lose the ticket. "Bornes libre service" are the ticket machines which are probably best avoided with foreign credit cards. Choose to collect the ticket at a ticket counter "guichet" instead.