Hi alhp,
Here are the search options. I presume that after going to
http://www.voyages-sncf.com you would have clicked on the "Train" tab at the top of the page.
On the left frame, you see the search options. Here is the screen capture.
http://i34.tinypic.com/2cqe9ty.gif
"Depart": Depart from (Paris)
"Arivee": Arrive at (Geneve)
"Trajet Direct Uniquement": If you check this box, it will search for direct trains only; that means there is no need to change trains. This is best for maximum convenience, but it is not necessarily the cheapest. It does help to narrow down the search results though.
"Nombre de passengers" means number of passengers. Note that if you put 2 or more, the price shown later when showing the lists of trains is the total price for ALL the passengers that is travelling. So if one ticket costs EUR 25, you will see that the price is EUR 50. Don't be confused; it's not EUR 50 per person.
Note that if you are under 26 years old, change the drop down box from "26-59 ans" to "12-25 ans". This means you get cheaper tickets!
1st class is only slightly better (in terms of comfort) than 2nd class. It is only slightly wider and having slightly more legroom, while usually being quite a bit more expensive; though if you are lucky, occasionally the cheapest first class ticket is cheaper than the cheapest second class ticket. The main difference in first class is that it is usually less crowded, has more space for luggage, and is thus usually quieter. But for all practical purposes, usually second class will suffice.
Once you have chosen your ticket, say that your country is "France", and after paying via credit card, you will need to enter your full name and date of birth as in your passport. Then you will have the option to download the ticket(s) as a PDF file. Keep this PDF file, print out the ticket, and bring the printout along, together with your passport. That is all you need.
Hope that helps. Let me know if you have further questions.
