Question regarding taking RER-B from CDG and Metro to Saint Paul

1) The RER-B is not an express. It makes several stops on its way into Paris. Always stay alert for theft anywhere on public transportation systems.

2) I didn't experience a crowd when I arrived, but the end of February is not July. I have a backpack and a duffel, so it's a little awkward for me. If you feel the need, move closer to the door as your stop approaches. If I remember right, there are buttons on the B's doors as on all the metro car doors. If no one else is disembarking (unlikely at Châtelet Les Halles' in July), just push it for yourself. There are map diagrams in the train cars, so you can follow your progress into town. Watch the timing of the doors opening and closing. They're fairly brief.

3) Once inside the CLH station, there are understandable diagrams with arrows to direct you. You're going to want the Metro Line 1 that's headed for Château de Vincennes. It is a bit of a walk here, but cars leave the stations every 3 to 5 minutes, so don't worry. You'll pass through one station, Hôtel de Ville, and then you'll get off at St-Paul, in the Marais neighborhood. You may have to punch the door button (or lift the lever) when the car stops. Be prompt when disembarking. Politeness is the rule. "Pardons" and "mercis" help get you on and off the trains.

4) Taxis are expensive. You can do the B train and the Metro. Enjoy the trip. This is Paris, man!

Almost everyone taking public transportation to the center of Paris takes the RER-B (unless they decide to take the Airporter-like bus to the Opera area or Montparnasse). Your first test will be buying the tickets unless you somehow get them in advance.

I've taken the RER-B many times and know that you won't be alone with wheelie luggage. Since you're getting on at the point of origin at Charles de Gaulle (CDG) airport, you'll have a pick of a seat. If it's really crowded (in July) it may be difficult to have your luggage sitting on the ground next to you. The French always have luggage racks for travelers. But, always keep your luggage close to you and keep an eye on your bags. Never walk away from them.

Depending on the time of day, stops vary. The RER-B is not an express train direct into the City. It looks like there are 12 distinct places the train may stop. You must keep an eye on the stops and know when to get off.
Here's a route map:
http://parisbytrain.com/wp-content/uploads/2008/06/b_jo_cdg.pdf

Chatelet-les-Halles is a major juncture for all suburban (RER) and Metro transportation. You'll have to make your way out from the RER area to the Metro level. There'll most likely be escalators.

Here's a link to the Paris Metro lines:
http://www.ratp.fr/informer/pdf/orienter/f_plan.php

I agree that the Metro 1 line towards Chateau de Vincennes is the direction that you want.
The challenge with the transportation in Paris is that there are points where there are a lot of stairs. Carrying luggage up and down the stairs is the issue. In Paris, there are many escalators that go deep, deep down to the Metro. The depths vary.

Just so you know: the French are sometimes quite gallant. And as a woman (probably looking quite exasperated or helpless), I've had a man help carry my bag up stairs. I'm very gratified that they are helping me rather than struggling up on my own.

Lucky you! The Marais is a delightful neighborhood.

My Recommendations for the Marais:

L'As de Falafel (the best falafel sandwich in the world); close 2nd is a cafe on a corner of the same street with a quieter old-world interior
Mariage de Freres tea shop and tea salon
Place de Vosges (covered arcade with art galleries, shops, a Damman Frere tea shop and a small park)
Wonderful boutiques on the Rue des Francs-Bourgeois (this is the major thoroughfare in the Marais)
Info:
https://en.wikipedia.org/wiki/Rue_des_Francs-Bourgeois
BHV Department Store is an old world gem of a place (http://www.bhv.fr/

Paris is a wonderful city to wander around....
If you need any other tips, email me.
Bon Voyage!

On our last trip, staying right near St. Paul, I wanted to avoid Chatelet les Halles because there seemed to be a lot of construction right then. So we took the RER B to the next stop, St. Michel. There's an exit from there, Cite, with an escalator, and, ta da, you are right there by Notre Dame. You can't be any more "in Paris" than that. There is a taxi stand as well in case you are tired or it's raining. When we arrived it was a beautiful day and we walked about 10 minutes to St. Paul.

A couple of clarifications:

Yes, there are express trains from CDG to Paris, but the first one doesn't leave until 8:54. Here's the schedule: http://www.ratp.fr/informer/pdf/orienter/f_horaire.php?nompdf=b_jo_rob&loc=horaires . The express are called a "direct", whereas the trains that make stops before Gare du Nord are called "omnibus". Watch the train board above the platform at the CDG RER to see what stops the next train leaving CDG will make.

At Les Halles you won't have a long change. Two metro lines are on the same side of Chatelet/Les Halles as the RER stops. Those are the 1 and the 4. There's one more that's new, which may be on that side of the station, too. All other metro lines are a hike away, but not the 1. Be sure to save your RER ticket because you'll need it to go through the metro turnstiles.

The only place you won't have an escalator is a short flight right when you reach the platform for your Metro train. It's only about 10 steps. Everywhere else you'll have an escalator, even the St. Paul exit, as long as there are no outages.

*Merci, everyone* for your helpful and sage advice. Especially, JohnK for reminding me of the buttons and levers to open the car doors. Joanna, I'm looking forward to experiencing your Marais recommendations. Karen, Merci, Merci, Merci for the excellent recommendation to take the RER B to St. Michael and avoiding the challenges of Chatelet Les Halles. Bets, I appreciate knowing how the direct trains work at CDG.
One more question: I was reminded to keep my RER ticket to use going through the Metro turnstiles. Do I also need to purchase a separate Metro ticket? I've read conflicting information.

It's the same ticket.

Unless the metro and RER have been reconfigured in the last year or I'm having an extreme senior moment, the A, B, 4 and 1 were always on the same side of Chatelet/Les Halles for the seven years I lived on the B and 4.

Then there is no long hallway and moving sidewalk. It's a fairly easy change, easy for Chatelet that is, from the RER to the 1 Metro. Gotta keep drinking that red wine to keep the memory going.

PNW google the parisbytrain website and it will walk you through getting to the RER station at CDG and show you what things look like. Its not that difficult to negotiate. The airport itself is the problem. Note that the ticket machines at CDG only take euro coins, not bills or credit cards so you'll have to buy at a counter if you don't have enough coins. Unless they've improved that since last year.

We took the RER B non-direct line from the airport around 0900 on a weekday last July, and it was neither scary or crowded. If you've ever been on the subway in NYC or metro in DC, its a familiar experience.

Thanks again.
Oh, now I understand where I'm going wrong. It's the color of my wine.

Well, it's time to add the blueberries, spinach, and carrot juice to the red wine. I indeed blew it. I finally looked it up on the RATP site, and the RER isn't on the same side of the station as the 1. How quickly, my memory repressed all those years of schlepping through that tunnel.

Karen's idea of crossing over the islands from St. Michel is a good one because you are walking in a diagonal.

Bets, I think that's proof that you've forgotten more about Paris than we'll ever know!

The airport itself is the problem. Note that the ticket machines at CDG only take euro coins, not bills or credit cards so you'll have to buy at a counter if you don't have enough coins

Here's a secret. Don't buy the tickets at the CDG train station counter. You'll be behind people asking "where do trains go?" and trying to pay with 3rd party checks from non-EU countries ;-) The only way the line could go slower would be to go backwards.

Instead, go to any of the many TI desks in the airport. See http://en.visitparisregion.com/practical-info/tourist-information-desks-100180.html for locations. They speak fluent English, they sell RER tickets and metro ticket books, they take US credit cards, and there's seldom anyone in line.

LOL re line at CDG for tickets. So true. In fact it is somewhat true at all train stations. Locals use credit cards and machines and so everyone in line is someone who doesn't speak French, is trying to pay in rubles or dollars or pesos, doesn't know where they want to go, or is trying to book a round trip to Guam. Slowest lines on earth. It took us over an hour to buy tickets to Vernon at St. Lazare (it was a day with only one sales office open) And it took us an hour to get our NDs charged at CDG (the machines would not take our credit card in spite of assurances to the contrary on line.