In France, post mail service is mainly run La Poste
If you want to send post mail, you will have to buy an envelope (in a La Poste office and supermarket/supplies store), write the recipient address and stick a stamp (to buy in a La Poste office or tobacconist shop).
The price of the stamp depends on the weight and the destination (France/abroad).
If you are concerned by the CAF (housing benefit) and/or the French Heamth Insurance, you are going to receive post mail.
Then, don’t forget to add your name on the mailbox or to indicate your room number on the Address part of your procedures.
If you want to receive packages, we advise you to let them delivered in a Points Relais (third place) to avoid theft in mail boxes.