Whatdo you know already about the Holocaust?

I have not ever researched about the Holocaust detailly, however I have heard of the tragic. It was such an nasty and discusting event. What I know is a brief story about it, and it is the Nazis from Germany killing most of the Jews. I heard there were lots of ways the Nazis killed the Jews, and the most known way how the Jews died were dieing by gas. The Nazis were to cage the Jews in a room and would open up the gas so that they will die. I hope this kinds of tragic doesnt happen any more.