Auschwitz, Dacchau and Buchenwald were "death" camps or "extermination" camps. The main reason a prisoner was sent to one of these camps was for extermination.
Zyklon-B gas was the cheapest, most reliable and most used method of murdering the victims.
Other methods of "gassing" had been used but proved unreliable.
First, the prisoners arrived at the camp by transport on a train. This meant loaded in cattle cars to the point that they were literally packed in so tightly that no one could sit or lie down. They were not provided with food or water during this trip and with one bucket for personal relief. After the train ride, those who survived were sorted out. Some prisoners tell of catching rainwater from the roof of the train in their hands so they could have a drink.
They were stripped naked and forced to stand in line after they disembarked the train. The inspectors would signal to the victims to go either to the left (death) for showers *zyklon-B was delivered in closed locked showers* or to the right (life) for work assignment.
Joseph Mengle was conducting medical experiments at Auschwitz, and of course one might be selected by him for medical experimentation which included being burned, being poisoned, having bones broken. He was a geneticist and was especially delighted when a pair of twins came through his line for selection. In my opinion Joseph Mengle was a monster. Two other doctors went to Auschwitz to conduct medical experiements on humans. Many women and children were killed and maimed at the hands of the three "doctors" who experimented on them.
The camp conditions were horrific. Prisoners were assigned to a barracks. Bunks were 4 beds stacked on top of each other with 18" of space between them. They were wooden slats. 4 prisoners to a bed. There were no matresses. The only bed-covers were red-cross issued woolen blankets. The barracks were not heated. There was no latrine facilities and only a bucket for relief in an entire barracks.
Prisoners were provided with rations of thin watery soup 2x per day and a piece of bread. Many starved. Disease was rampant. If a prisoner were too sick to report for work, that prisoner quickly was exterminated.
At the liberation of Buchenwald, human beings were literally stacked like cord-wood waiting for the flames. Some of them were not quite dead yet. The SS guard wanted to "get rid of the evidence" before the Allies liberated the camp.
Many prisoners were so sick with dysentery, cholera, or typhus that there was nothing that could be done for them but show kind humanatarian aid to keep them as comfortable as possible. Some were so malnourished that they could not eat normal food but had to eat a liquid diet until their systems recovered enough to eat a normal diet.
So, life for the prisoners at Auschwitz or Buchenwald would have been a trial of endurance. Imagine life in hell.