After the invasion and surrender of France, most of the French POWs were held in camps called Frontstammlager (Frontstalags), which were distributed throughout northern France. These were essentially transit camps, comparable to the Durchgangslager on the Eastern Front, where prisoners were temporarily housed for a few weeks to a few months before being transferred to permanent prisoner of war camps (Kriegsgefangenen-Mannschaftsstammlager, or Stalags, which were enlisted men's camps; and Offizierlager, or Oflags, which were officers' camps). However, some of the Frontstalags became long-term internment sites, where prisoners were held for several months or even years; this was particularly the case for colonial prisoners from French North and West Africa, whom the Germans didn't want to bring to camps within the Reich due to reasons of racial policy.

The Germans had initially intended to repatriate French POWs to France after the conclusion of a final peace treaty with the Allies, which obviously never happened. As it stood, there were about 1.8 million French prisoners in German captivity. In general, the Germans treated French POWs (and other Western Allied POWs) decently and followed the requirements of international law regarding POWs. The conditions in the Frontstalags varied from camp to camp; most of the camps were located in former French army barracks, so there was reasonably good infrastructure in place, although the quality of food and medical care was inconsistent, particularly early on as the Germans struggled to cope with the huge numbers of POWs they had captured. After the first few months, conditions improved significantly, both because logistics had improved and because most prisoners had been transferred out of the Frontstalags, relieving the problem of overcrowding.

Within the Stalags and Oflags, the French POWs had well-organized communities, which were led by appointed "men of confidence" (hommes de confiance). These communities supported a wide range of cultural activities, including sports, orchestras, theater groups, libraries, and educational courses; the Red Cross supplied the prisoners with books, sporting equipment, and other things to support these activities. French prisoners had enough leisure time that famous French cultural figures were able to do important work in the camps; Jean-Paul Sartre wrote his first play as a POW at Stalag XII D, Olivier Messiaen wrote his Quartet for the End of Time at Stalag VIII A, and Fernand Braudel wrote most of his seminal work, La Méditerranée et le Monde Méditerranéen à l'Epoque de Philippe II at Stalag XII B. The French prisoners were among the most politically active groups in the camps, with most of the prisoners being actively opposed to the collaborationist Vichy regime, despite German attempts to spread pro-Vichy and pro-German propaganda among the prisoners.

Of course, it wasn't all fun and games. Most enlisted French POWs (more than 90%) were sent to work in labor detachments (Arbeitskommandos) and spent most of their time outside the camp working; officers couldn't be compelled to work under the Geneva Convention, but the Germans often forced NCOs held in the Stalags to work anyway. Initially, French POWs were mainly used for agricultural labor, although some were sent to work in mines or in German factories. Working in the mines and factories was generally more dangerous, both because the work itself was more dangerous and because the factories were often targets of Allied air raids; the Geneva Convention prohibited the use of POWs in war-related labor for this reason, although the Germans largely disregarded that provision with prisoners of all national groups.

The colonial French prisoners generally fared worse than their Metropolitan French counterparts. Most of the 120,000 or so colonial prisoners were held in the Frontstalags in France throughout the war. They were subjected to racial abuse by the Germans, and the Germans are known to have murdered groups of colonial soldiers during their surrender. The colonial prisoners presented a unique challenge for the Germans, because they often fared poorly in the cold weather in northern France, having been used to the more tropical climates of their homelands; the Germans often moved colonial troops to camps in the south of France to get them to a warmer climate, and by the end of the war, about 75% of the colonial troops had been repatriated. French colonial POWs weren't subjected to systematic racial persecution on the same scale as Soviet POWs were, but they still experienced worse treatment than other French POWs did.

By the last year or so of the war, the pressures of the war on the German economy led to a decline in conditions for all prisoners of war in Germany, regardless of nationality. Food supplies became scarcer and prisoners were more reliant on parcels of food supplied by the Red Cross. The quality of medical care deteriorated and prisoners were exposed to the danger of Allied air raids; obviously the Allies didn't target POW camps during bombing missions, but stray bombs sometimes hit camps or forced labor units.

In the end, out of the 1,845,000 French POWs captured by Nazi Germany, about 51,000, or just under 3% died in captivity. This is a bit lower than the death rate of 3.6% among British and American prisoners, and obviously much lower than the 58% death rate among Soviet POWs. As far as I know, these figures don't include the 1,000-1,500 colonial prisoners who were killed by the Germans after surrendering during the invasion of France. In any case, the French POWs experienced one of the lowest death rates of any national group in the German POW camp system. Obviously, that doesn't gloss over the difficulties and privations that many French prisoners experienced, particularly in the first and last months of their captivity, but it's another illustration of the stark contrast in Nazi racial policy toward POWs.

Sources:

Yves Durand, La Captivité: Histoire des Prisonniers de Guerre français, 1939–1945 (FNCPG, 1980)

Yves Durand, Prisonniers de guerre dans les Stalags, les Oflags et les Kommandos 1939-1945 (Hachette, 1994)

Raffael Scheck, Hitler's African Victims: the German Army Massacres of Black French Soldiers in 1940 (Cambridge UP, 2008)

Raffael Scheck, "French Colonial Soldiers in German Prisoner-of-War Camps (1940–1945)", French History 24, no. 3 (2010).