I have purchased my train tickets for France and I printed my tickets at home on my computer. Do I need to validate them before boarding the train? And if so, how do I do that?

Tickets printed at home usually have your name, date of travel and other information that make the ticket invalid for any other travel time. You should not have to validate it.

When the conductor checks your ticket on board, however, he may ask you for your identification.

Prob not necessary, but to answer the question about how to validate in general, you look for yellow boxes on posts around the train stations. I think there's a slot to stick the ticket in and it will be punched/validated. Though slot may only be big enough for the standard ticket from the station rather than one printed on a home printer. I'm sure someone else can clarify.

Michael and Sidny are correct. All the information the conductor will need to see is printed on your tickets and the machines only accept standard-sized tickets.

No, you don't need to composte the preprinted tickets. You do need to have a photo ID with you to prove you're the person the ticket was issued to in case the conductor asks.

Absolutely no validation of self-printed tickets.

what if they are full fare tickets that are presuambly fully refundable or mostly refundable - or cannot even full fare tickets be refunded after the specific train departs (this is the case I gather but thought I would ask for my info - merci)