When you're issued a French long-stay visa, you have to report to the OFII, which is the French Office of Immigration and Integration, during the first three months of your arrival in France. This requires first mailing a form to this office right after you arrive in France and then setting up an appointment to confirm your presence in the country and have a physical exam done.
You're given an 8, 9, or 10 AM time slot at a clinic near the Place de la Bastille, along with a bunch of other people, so even if you arrive on time there's already a long wait. Almost three hours in our case, which we heard is standard. The physical consists of being weighed, measured, having a chest X-ray taken, and answering some standard health questions to one of their doctors. After confirming your address and a few other things they put another big stamp on your passport and you're done.
Since we don't have an actual resident visa, just an extended-stay visa, we were spared from having to attend the Integration session, where during an entire day they give formation civique, a civics education class on the rights, principles, and values of the French Republic.