This is not a stop over but just a connection. And for your bag, you do have to collect it in LAX as this is your entry point in the US, go through customs and re-check (as it will be already tagged to LAS, the re-checking operation just consist in putting the bag on a belt). You won't need to collect it on the return trip (it will be transferred automatically to your flight to CDG).
After immigration and customs, you'll have to go to your connecting terminal. I suppose you connect on DL ? If yes, no need to re-check with DL as you will already have your BP (you can go straight to the gate).
The only tip we can give you is to try to be seated as much from as you can in the CDG-LAX to exit first and reach immigration as quickly as possible.