Train line

Hi Amy,
 
There's a train station in Ville d'Avray called Sevres-Ville d'Avray which is serviced by two train lines, Transilien L and Transilien U.
 
Transilien L trains will travel to Gare Saint Lazare in Paris, which is connected to Paris Metro line 14 which travels north west to south east through the center of Paris.  So taking Transilien L train into Saint-Lazare is the fastest way to get into Paris, with an easy connection on Paris Metro line 14 to further center into the city.
 
Transilien U trains stop and end at La Défense which connects to both RER A and Paris Metro line 1, both which travel west-east through the center of Paris. 
 
Transferring at La Défense to RER A in direction Marne la Vallee or Boissy-Saint-Leger will also get you to the center of Paris (Charles de Gaulle Etoile, Auber or Chatelet les Halles stations are popular).  Transilien U + RER A is the 2nd fastest way to get into Paris with some interesting tourist stops available along the line. 
 
Finally, Transilien U + Paris Metro line 1 from La Défense in direction Chateau de Vincennes is the slowest option but will stop right at Louvre and other very central stations on its west-east journey.
 
Single-use RER ticket prices for any of these trips will be 3.65€ and you would use that to transfer from Transilien to RER or Metro.