CDG is big - it has one huge terminal and 2 smaller ones. The train station isn't huge though, and if you're arriving at terminal 2 its in the middle of the main gates, so its only 10-15 minutes walk. From terminal 1 you need to add a little more time, as you need to take the internal train service between terminals (this runs all day).
I've never got lost in CDG yet - its just like any other airport, the signs are the same

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You might be cheaper (and it will be more convenient) using a shared shuttle though, especially if any of your TGV times are in a peak time period. Thats what we did earlier this month, booked a shared shuttle from CDG to DLP wth RStransports, then took the TGV back.