Simone is interviewed, and she talks incessantly, confidently and smartly. Lighting cigarettes, answering seriously to questions like "has pessimism destroyed your life?" she proves her brilliance.
There are also shots from tertulias with her and Sartre, who is more laydback than her, and other french intellectuals from the time, smoking, playing the piano, and most importantly, discussing literature and politics. The way they interact, with that old-mans-dignity which was comme-il-faut before the 1980ies is just fascinating and extremely appealing.
If you never were able to read Simones books straight through, you should watch this film to catch some of the atmosphere it was created in. It might help and it's certainly fascinating to watch them.