Steve, since you have been most likely unnecessarily confused, let me summarise if you are arriving at CDG on UA at T1:
- deplane, take moving walkway to immigration
- clear immigration
- take escalator to baggage claim (CDG has signage telling you how many minutes until your bags arrive)
- exit baggage claim by walking through customs
- look for signage to 'niveau CDGVal' (* you may want to make a detour to a cash machine if you haven't brought any cash with you at this point)
- take CDGVal to Terminal 3-Roissypole for the RER
- exit CDGVal to the station
- purchase tickets; your US issued credit card will most likely not be accepted if it has no chip; you can use notes but if you need coins for some reason then you can purchase at the window
Note that there are actually two different RER stops at CDG; one serves Terminal 1 and 3 and is at Roissypole; the other serves Terminal 2 and is at the Gare SNCF.
As you are flying UA, if you are in C or F you may be able to take advantage of a little-known fact that you can use a meeting room converted into a shower room with rollaway bed at the Sheraton in Terminal 2 for 45 minutes to shower and relax. For people flying into Paris as a visitor this is a great free option as your hotel room may not be ready that early. (They allot 45 minutes per person but couples have reported that they are able to share the room for 90 minutes total) You said in your first post that you are going to Terminal 2 so I think that you may already be aware of this option.
If you are going to use that option, get off at Terminal 2 and look for the Sheraton on the upper level near the Paul Boulangerie kiosk. Then when you are clean and rested, buy your RER ticket from a green kiosk (yellow is SNCF) and use the RER to go into Paris. At Terminal 2 the ticket machines are free-standing kiosks, unlike at most metro stations where they are built into a wall. They also serve multiple functions so yes, you can purchase the RER to Paris ticket as well as multiple metro tickets there.
(Even if one isn't going to shower at the Sheraton, I like the RER station there better as it is brighter, more refreshment options, and generally more people around who are willing to assist as they are waiting for their long-distance trains etc. I've helped countless tourists there with ticket purchases. It's a really short detour to end up there instead of Roissypole)
And not to further confuse you, but a Navigo Semaine runs from Monday to Sunday and is 34,40 for the week for zones 1-5, which can be used on the RER to/from CDG. As a visitor you can purchase Navigo Découverte. Depending on your days of travel and the places and amounts of travel you expect to do, it may be an option to consider)
http://www.ratp.fr/fr/ratp/c_20597/f...is-et-semaine/