Wayne,
I rented a car for the first time 2 years ago driving from central Paris to Normandy to CDG. I was also nervous about the rental car return and had to do it late at night past midnight. It's actually very easy/straightforward going back to CDG. As several others have noted, it's simply "follow the signs".
A few things I learned... it's almost imperative to have a GPS device especially if you're not familiar with the roads. I brought one from home loaded with Europe maps which helped me navigate. One mistake I made was not filling the tank earlier before I got close to CDG. Please note the self serve pumps at most gas stations only take credit cards that are "chipped". Most US issued credit cards have not been converted. You could ask for one.. the chance of getting one depends on the credit card company.
I ended up paying an arm/leg for gas because I couldn't find a gas station open late enough with cashier who could take my non chipped credit card. I had to return the car with empty tank.
Hope this helps!