They were systematically murdered, or at least as many of them as the Nazis could get ahold of. This was policy in the Third Reich, called "The Final Solution" - and the plan extended beyond Europe, had the Nazis been victorious. Hitler referred to it as "ridding the world of the scourge of International Jewry".
People who were not Jews were treated differently than the Jews in Nazi Germany. Some of the Jews were German citizens but they were treated as Jews.
It depended if they were Nazi's or not, but some Nazi's were forced into it. Some did, some didn't.
Hitler was a Nazi. He killed Jews.
Research Kristallnacht and the Holocaust. Bottom line: Beyond Terrible.
Hitler decided to gas the Jews in nazi Germany
Hitler's Nazi Germany invaded many European countries. Where a Nazi-friendly regime was installed, the Nazis could get some of the locals to point the finger at Jews, thus the Jews could be rounded up and transported.
Hitler's reason behind the Holocuast was that the Nazi's blames European Jews for the condition of the economy.
Most European Jews ( The ones in Nazi occupied Zones) were denied theirs once legal state protections rights because the Nazis and Hitler marked Jews as "Undesirables", "Sub-Human and "Anti-German." This means that Jews were hated by Hitler and Hitler passed an Law which means all Jews in Nazi Zone are legally state less people and the Nazis can do anything they want legally.
Concerning European Jews: Hitler did not just kill European Jews. During the Occupation of Tunisia, he also began killing Tunisian Jews. He would have tried to kill Moroccan Jews as well, but King Mohammed V resisted. However, he was only able to kill those Jews who lived in countries that Nazi Germany was able to conquer, which were mostly in Europe.Concerning Jew-Killing: As for why Hitler killed Jews at all, please see the Related Question below.
Lies.
Poorly.
The Nazis killed and slaughtered about 6 million Jews.