Hitler had a seething hatred for the Jews, and blamed them for most of Germany's economic and social problems. After he came to power, Jewish families were split up and sent (at first) to labour camps and (later) to death camps.
Long story short, he didn't treat them like humans. He treated them like insects that needed to be squashed.
As many as two-thirds of Europe's Jews were killed during the Holocaust. Other groups, such as gypsies, the mentally disabled, and the handicapped were also killed. Many victims were killed in mass, open air shooting, especially in the then Soviet Union (Russia, Ukraine, Belarus) and were not sent to camps.
The proportion varied considerably. At the extermination camps (Auschwitz-Birkenau, Chelmno, Treblinka II, Majdanek ('new section'), Belzec and Sobibor very few survived. At these camps most victims were gassed soon after arrival. A handful of Jews at these camps were forced to help in various ways with the extermination process, for example, by dragging the corpses to the crematoria or mass graves. Some of these survived. However, there are only two(!) known survivors from Belzec, where according to the SS's records, 434,508 Jews plus an unspecified number of Roma were killed.
At Dachau, which was mainly a camp for political opponents of the Nazis, an estimated 25,600 died out of 150,000.
The word "survived" needs defining carefully, otherwise one ends up talking about quite different groups of people. The usual meaning of the expression "a holocaust survivor" is someone who was sent to an extermination (death) camp, concentration camp (or equivalent), but was still alive at the end of WWII in Europe or when the camp was liberated. (In other words, Jews and others who had managed to flee to countries like the U.S., Britain and Sweden before the start of World War 2 are not included). The most common figure is about 200,000. Jews in hiding who survived also count as survivors.
Incidentally, the criterion 'left the camps alive' is trickier than one might think. Some Jews were moved from one camp to another. Anne and Margot Frank, for example, were moved on 30 October 1944 from Auschwitz to Bergen-Belsen. So they were alive when they left Auschwitz, but died of typhus at Bergen-Belsen in March 1945.
Once one was actually in an extermination camp system the chances of survival were remote. It needs to be noted that there were different types of camps, ranging from 'punishment camps' like Dachau to extermination camps. From 1939-40 onwards the SS graded the camps into three types, I, II and III and later added the extermination camps. There was not much difference between types I and II, except that the prisoners were usually better fed at a camps graded I. At grade III camps most prisoners had to do very hard manual labour on grossly insufficient food and were worked to death. At the extermination camps, nearly all the prisoners were shot or gassed soon after arrival. For information: Dachau was a grade I camp, Buchenwald was grade II, Auschwitz I (old section) was grade III, while Treblinka, the Birkenau section of Auschwitz, Belzec, Sobibor, Chelmno and the newer part of Majdanek were extermination camps. Obviously, one's chances of survival at Dachau were much better than, for example, at Treblinka.
== == Jews, Gypsies, the Disabled, Homosexuals and Dark-Skinned or Mixed-Race people.
They had do eat whatever they could. I could imagine it would be bugs, or lint. But at the most, It was whatever the Nazis gave them. Stale bread with some thick soup. But they never gave that every day.
Suvivors like Elie Wiesel had seen the separation of their familes. That was all too painful, he wanted to be reunited with his mother and his sisters. He saw the death and wanted to survive. He wanted to see them again and he wanted to survive Hitler. Others considered the camps as one of Hilter's games or tricks they wanted to outwit him and survive. They made friends and tried to be with family members in the camps. They looked forward to eating and living.