I am brand new and need help!

We are planning a trip to France & Italy in September. We will be arriving at CDG(Paris) airport and had hoped to go directly to Giverny. Can anyone help me with the best way to do that? I don't know if we have to take a train to Paris first or if we can go directly from the airport. Or perhaps, we will need to rent a car at the airport. Any advice will be very welcome!

Thanks, Ann