Air France has multiple lounges at CDG, they vary in amenities and quality quite a bit, so it's best not to conflate them all. They are also scattered across multiple parts of the airport, and it is not easy (sometimes impossible) to get to some of them. The lounge(s) that will be available to you will depend on what gate your flight(s) use (there are lounges specifically for arriving passengers, others for departing and transit passengers), and of course what exactly qualifies you to use the lounge. It's a complex mix, so best to be specific.
As you might imagine, access to lounges is restricted (the better the lounge, the greater the qualifications to use it). Generally speaking, I believe access is limited to business class passengers and above, or elite level status in Air France's FF program, and some additional options (those who hold one of the premium Air France or partner credit cards). I would not expect that they're open to those traveling in economy or economy plus (whatever it's called), unless you have elite status or some other qualification.
You can usually (not always) pay a fee to use the lounge (depends on the lounge, may also depend on how crowded it is; lounges tend to be on the crowded side lately, as everything is).
You can always just show up and try to get in, but the lounge dragons are quite effective at keeping out those who don't qualify. If you want to arrive armed with a solid understanding of your options (and given the dizzying complexity of CDG, that's a good way to arrive), I'd suggest posting in the Air France forum over at Flyertalk. You'll need to provide your own details, but you'll get complete, up-to-date and accurate info on what you can expect.
Bonne chance!