Don’t count on the people behind the counter. It has been a while since they are not selling tickets any more. The ticket machines accept cash and cards, speak English and will guide you. Buy a single ticket or a “carnet” (book of 10 tickets) or think about a “paris visit” transport pass. This pass comes with a lot of reductions. Ask yourself how many of these reductions you really need, then calculate, then buy a “carnet”.
On the map next to the ticket machines, find the closest métro station to your destination, the métro line and the terminal of your direction. In every station, every line stops at individual platforms, one for each direction. Changing lines always means changing platforms. Keep the right direction in mind. In order to literally be on the safe side you will find a sign with all stops next to the stairway.
Now slide a ticket in the slot of the gate, pick it up as it pops out and keep it apart from its unused brothers to find it quickly in case of ticket controls. The tickets may be used in the métro, the busses, the RER within Paris. A ticket is valid 90 minutes in the bus he bus and 120 minutes in the métro. Within this time you may change trains or buses as often as you like without having to pay again. Bus and métro, however, can n o t be combined with one ticket! When you leave the public transportation network or the bus your ticket becomes invalid and you better let the next waste bin take care of it. It is difficult to distinguish a used from a new ticket and you don’t want to get snapped at by a machine and cause a jam because you slid an invalid ticket in the turnstile.
In the trains, all stops and connecting stations are indicated. When you arrive, consult the large-scale “plan du quartier” which will help you to find the closest exit for your destination.
I prefer the bus to the métro. Besides the fact that every bus trip in Paris is a sightseeing-tour the buses take their time but save you a lot of tiring underground kilometers and even more stairs!!!!
This is not more than a very general approach. Contact me if you have questions!