You may reach Paris by train from neighboring European countries. You might arrive at one of several train stations (Gare du Nord, Gare de l’Est, etc.) but they are all inside Paris, directly connected to the subway system: see RATP for planning your trip from there.
Paris has two airport: Roissy / Charles de Gaulle and Orly. The first one is located North of Paris, the second one South. Either way, you can reach Paris from the airport by taxi, bus or train.
Depending on where you’re staying in Paris, and on your budget, you may choose from various options, combining buses, suburban train (RER) and perhaps subway.
You can reach Paris from both airports via RER line B, which stops in the center of Paris, with St Michel station being close to the conference venue. RER B trains have various schedules, with some trains not stopping at some stations. However, all trains stop at stations inside Paris (from Gare du Nord to Cité Universitaire) so you should not have to worry about it.
Complete list of public transportation options are available on Aéroports de Paris’ website, for Charles-de-Gaulle and Orly airports respectively.
The system is standard for occidental countries. Just plan for the likely case where the driver does not speak good enough English.
More information, including standard fares, may be found on Aéroport de Paris’ official site, for Charles-de-Gaulle and Orly airports respectively.
Paris has an excellent subway and bus network, operated by RATP. The same (subscription) tickets work on bus, metro, and streetcars. If you stay for the week you may consider to buy a weekly subscription: it starts on Monday and ends on Sunday, costs 22.15€ and is valid on the whole regional network, Versailles included (bring a photo with you to get it).
You can plan trips on the RATP website, where you can also find an interactive map and fares information. RATP also offers smartphone apps for planning trips and planning touristic visits.
Credit cards are commonplace in Paris and ATMs may be found easily. It is however advisable to carry cash for small purchases, e.g. many bakeries won’t accept cards under 10€.