It is fairly easy to navigate the metro system in Paris. You can check out the RATP website that others have mentioned above...they have maps, etc. that you can use to get oriented. This site has a Paris Metro Guide that can help you figure out how the system works as well.

Thank you everybody! Your replies have given me a more peace of mind about commuting to CDG to Gare du Nord. :o)

Hello, guys. Sorry for my off-topic, but I'd like to ask you a question about the Metro and RER. Should I have a ticket every time when I change line..I mean if I want to reach a place with line 5, but I'm on line 6, should I have two tickets...once for the line 5 and once when I take line 6...
I'm sorry for this stupid question, but I've never been in Paris and I plan to go soon, so I'd like to know these things...
Thank you

Even a German/English speaker (me) can get around on Metro. It's not a dumb question. No worries. You'll be fine. Have a great trip.

Oh, sorry #12, you don't have to use a new ticket for transferring w/in a specific system (i.e. 2/3 trains w/in Metro), just be sure to watch the signs leading to the line you want, and don't go thru the exit gate 'til you get to your destination.
Paris is a wonderful city. I don't get to go nearly often enough. :-)