Antisemitism is racism, but specifically against anyone who is either a practising Jew or of the Jewish race. Although Arabs are semitic, the term antisemitism is used to refer specifically to Jews.
This racism takes many forms including conspiracy theories of Jews controlling banks and governments, or a more modern form is to make false or exaggerated stories and claims about the Israel/Palestine conflict, in order to use as a weapon of de-legitimisation against the Jewish state. Or others include simply denying the Holocaust or the Jewish connection to Israel; which is a bit like denying that slavery ever happened or black Americans and Afro-Caribbean people's connection to Africa.
from the ritual, (Christian) antisemitism started when Christianity was merely a branch of Judaism and the Christians did not like all of the ritual and ceremony involved in Judaism. Though there was a lull in the second and third centuries, the persecution has gone on since. Naza antisemitsm is arguably the natural progression of Christian antisemitsm, though the Roman Catholic Church would argue against it (they would also argue that Christian anitsemitsm does not exist). i hope that answers your question.
well, he promissed that if the Jews started another war, then it would lead to the destruction of the Jewish people. Which is implicitly saying that he will kill the Jews, there were many reasons given for wanting to kill the Jews. But the truth is often much more simple, attached is a long list giving reasons as to why the Nazis (and Hitler) hated/wanted to kill the Jews, but most of them are irrelevent: antisemitsm started before the Nazis and continued after the Nazis, if there was a global Jewish conspiracy, then they would have done something to help the Jews of Europe. Hitler knew that the Jews were defenceless and harmless, they were killed for political reasons, they were killed because that is what made the people happy and kept the Nazis in power.