Overall about six million Jews were killed in the Holocaust. About half of the victims were killed in extermination camps and concentration camps, and the other half in mass open air shootings 'in the field' and by starvation in ghettos.
Hitler and the Nazis did not bury the Jews that they killed. The Jews who were killed in the concentration and extermination camps were cremated. Others, who were shot, had to dig mass graves themselves and they were then killed in such a manner that they would just fall into the mass graves.
The total number of Jews killed by the Nazis was about 6 million. Just over half of these died in extermination and concetration camps. The others were killed in mass open air shootings or perished from starvation and disease in ghettos.