It is relatively well known what life was like for those inside Nazi concentration camps. We on Reddit even had the opportunity to speak to a Holocaust survivor not long ago. How did normal Nazi prisons compare to death camps operating at the same time, under the same regime?

I answered a question that led to a response that might be helpful here

The difficulty is that the Nazi system of camps was rather chaotic. Hence, each camp commandant might do things differently and all that mattered was if it "worked". Hence, only in occasions where there was one plan, such as in the Operation Reinhardt camps, were the camps similar enough to truly call them the same. Nevertheless, we can still divide the camps, as I did in the aforementioned link, into three types: concentration camps/work camps, death camps, and combination camps (Auschwitz).

The differences among these three types of camps were in purposes. Concentration camps were where political, racial (sometimes), and traditional criminals were sent. You could be, especially early in the regime, released from such camps depending on the reason you were incarcerated. These camps worsened in treatment of the prisoners all the way until liberation before which camp transfers from Auschwitz, which led to disease and overcrowding, gave us the images that we recognize today of mounds of corpses and burial pits. The concentration camp system was horrid, but it can be differentiated in that the purpose was not the complete extermination of the inmates. Many died and many were murdered. Conditions were extreme, but there were no extermination processes at work (ie. No gas chambers used, no exterminations of an entire group at the camp, etc.).

Death camps seem to be the focus of your question. We do know what life was like in the death camps because the Nazis used sonderkommando (Special Commando or Special Worker) to do the menial tasks of the killing process and used others to sort the materials of those exterminated. These were usually Jews who were forced into such labor. A few managed to escape from Aktion Reinhard camps (which I discuss here) and lived to tell of the killing processes there. Life was difficult for these inmates, but sometimes not as bad as life at a typical concentration camp because they could procure food from the clothing of those who had been killed.

The same is true of our knowledge of Auschwitz II Birkenau (the part of Auschwitz with a death center). Sonderkommando who escaped during the evacuation of Auschwitz give us our understanding of what it was like there. The sonderkommando were selected by the Nazis from among the Jews who arrived on trains for extermination. This meant that their first task was often to cremate the bodies of their families and friends with whom they had just arrived. A great number of them committed suicide by "attempting escape" or by flinging themselves into the electrified fence. Those that did not often described themselves as robots and not truly men. They believed that they would die and indeed the Nazis purged the sonderkommando every six months or so.

Life in the extermination portion of the death camps consisted of roughly 12 hour shifts every day. One might have the job of "escorting" victims into the area in which they would be told to hang their clothes and prepare for a shower. They would then cram as many into the shower area as possible. Others would be charged with removing the bodies from the shower area. Next, gold teeth and other valuables would be extracted and the bodies searched. The bodies would then be taken up to the crematoria by sonderkommando and burned. Sometimes outdoor burnings occurred. One sonderkommando managed to get a camera and somehow snapped some pictures here, here, and here.

The sonderkommando would then rest, eat, and drink. They, evidently, had more freedom at Auschwitz than prisoners of the work portions of the camp and were sometimes left to their own devices.

This is a brief description of the life of sonderkommando. If you have more questions, please ask for any specifics.

Sources

Bezwinska, Jadwiga and Czech, Danuta. Amidst a nightmare of crime; manuscripts of members of Sonderkommando Panstwowe Muzeum w Oswiecimiu, 1973.

Grief, Gid'on. We wept without tears : testimonies of the Jewish Sonderkommando from Auschwitz London : Yale University Press, 2005.