Adolf Hitler was the creator of the Nazi party and then the ruler (Fuhrer) of the Third Reich. He based his ideology on works created by Nietzsche - German philologist who created the idea of people who are destined to rule over other people. Those super-humans were supposed to have the immunity for committing some crimes because they would do those only for the higher good of millions, Nietzsche would say.
Hitler saw himself as such person, he actually went a little bit further and invented the idea of Germans being the descendants of Aryan race, which for Hitler was the Master Race. Therefore, his policy during the WWII and before was to clean the world from sub-races like Jews, Gypsies and Polish for example. He thought that sub-races were useless and would make no good in the world of tomorrow which he had woven in his mind. The rest of the people were supposed to be used as work forces mainly as they weren't as polluted and useless as the sub-races. Those would be the people whom the Aryan-German race would rule upon.
That's why Hitler, along with his Third Reich, created the extermination camps, with the biggest one situated in Poland in Auschwitz (from ger.) or Oświęcim (from. pol.). In those camps people were being held and treated as animals for the very sake of the Nazi ideology. Most of the Jews brought to concentration camps were exterminated just after leaving the wagons they had been brought in. Mass extermination was performed using poisonous gas - Cyclon B. People were told that they're gonna go to the shower rooms to clean themselves up but instead of water, Nazis were throwing to those shower rooms cans with the poison. After about 10~15 minutes dead bodies were being transported to the furnace rooms and burnt.
In about 12 thousand concentration camps, Hitler and his people killed about 11 million people (out of 18 million who went through the camps).
To sum up - Hitler's aim was to take control of the world and rule it from his "iron throne". However, Hitler's world was a world free of all Jews, Gypsies, Catholics, Poles and many more who were in his way.