Will anyone actually read a review of the BnF in English? Well, if you do, you might just be a…read morenervous anglophone grad student wondering how the hell to approach this massive French monument to scholarship. If that describes you, I have some advice. Get out now. Study business or social work or something practical.
Now, that said, I have actually helpful advice on how to make use of the BnF if you insist on getting your Ph.D. in French blah blah blah like I tried do do a few years ago. (Big mistake, see above.)
In order to use the library just as a work space, you can access the Haut-deJardin areas by purchasing a one day ticket for around 3 euros. Scan the bar code on the way to your room of choice and set up shop. Be prepared to be surrounded by giggling undergrads and high schoolers, unless you can get a place in Salle D, which is the law and business section (see above).
Keep in mind that there is no wifi at the BnF. The unions fought against it because who knows? Those wifi signals could be dangerous to your health! (I'm not joking.) In some rooms there are ethernet cords, which are not at all dangerous unless you decide to strangle the high school kids with them. You'll need an annual card, not just a daily ticket, to use the internet on your own computer. If you just want to check email, you can ask the employee at the desk to "Commencez, s'il vous plait, une session internet" and then point at one of the common computers.
If you actually need to use a book or two, keep in mind that this is not a lending library. If you can find the book in the catalogue, see if it is available in Haut-de-Jardin. If so, you find the room it is in, go there, take the book off the shelves, and read it right there. You can't take it with you, or even take it into another room where another book you need to look at is found.
If the book is only available in the "magasin," this means that it is not available to the general public, only to researchers. But wait! You are such a researcher!
To get a card giving you 15 visits or annual access to the research library Rez-de-Jardin, you will need a letter from your institution that details your research, or proof that you are faculty at an institution of higher learning. You may also be asked to prove that you need access to a resource that is ONLY available in one of the collections that is open only to researchers. This should be easy. Choose something old and rare that they have not yet digitized from their catalogue. Be sure to do this before you sit down for your interview.
Another tip is that if you are planning to get a researchers card, it is sometimes easier to do so at the Richelieu site in the 2nd, although this might just be apocryphal grad student gossip.
Once you have the card that allows you into the bowels of the BnF, prepare yourself to experience the act of scholarship as alienation. After making a reservation to sit at a particular place and ordering books for the day, you will ride two long escalators into the glass tomb that is Rez-de-Jardin. The enclosed garden is just sad. The cafe is even sadder. There used to be a smoking room which was the saddest place on earth; at least that's gone.
You pick up your books at the counter of the Salle in which you have reserved. You read them in total silence. At the end of the day you can put them aside for tomorrow. That is, if you decide to ever go back.