I'm a little confused. I'm using the Web site ParisByTrain.com to figure out transportation in Paris. Specifically, I'm trying to figure out how to get from the train station Gare d'Austerlitz to the RER station Haussmann St. Lazare. There is a feature to put in your starting and ending points and they tell you how to get there. I'm not sure I understand the results. Is this Web site saying that there is a train from Gare D'Austerlitz to Gare St. Lazare?

Go to : GARE D'AUSTERLITZ - NOCTILIEN
Direction : GARE MONTPARNASSE.
from : GARE D'AUSTERLITZ
to : GARE SAINT LAZARE (36 minutes)
Go to : Haussmann-Saint-Lazare - RER (5 minutes) *** I think by walking
Transit Fare Zone(s) : 1

I used the Paris public transit site, ratp.fr.
They have an "English version" site.
They indicate it takes 19 minutes, all in.

Use www.ratp.fr.

Isn't "Noctilien" the late-night bus service, with limited routes? Did you indicate a departure time after, say, 1:30 a.m?

When you use the RATP site, be sure the date you enter is for a weekday or a Saturday or a Sunday (whichever you will be making that part of the trip), the date/time have not already passed in Paris, and the time is close to when you think you will be going.

You entered the wrong time of day, no doubt, as that is a night bus. The results are simply showing you a night bus between the two points, that's all (Gare Austerlitz to Gare St Lazare), which takes 36 minutes, then you have to walk five minutes from the bus drop-off point to the RER station, which is not right near that train station's metro stop.

There are lots of other ways you can do it. Such as just taking the RER from Austerlitz to Invalides and then metro line 13 to Gare St Lazare. It's probably a little closer at the endpoint to take the metro from Austerlitz to Republique, transfer to line 9 and get out at the Havre Caumartin stop. Well, it's probably about the same distance walk to the RER stop as from the train station.

I assume you have a reason to go to that RER stop, which is only the beginning point of line E which doesn't really go anywhere from there except out of town to the NE.