>Why do people believe Christ was the messiah and not just a cult leader?
Faith, among other things. Just like Jews believe all their beliefs.
>What are all of those denominations?
Protestantism. Tons of churches, groups, cults...
Catholics have the Roman Church and some smaller Eastern Catholic Churches like the Copts or Byzantines. Basically they believe the same things but they have their own Rites, traditions, and cultures.
Orthodox consist of churches set up around an ethnic group, example: Russian Orthodox, Greek Orthodox, et cetera. They are collectively the Eastern Orthodox church and they are all in communion through Patriarchates.
>What's the difference between Catholic and Protestant?
Protestants believe the tenets brought forth by Protestantism. Luther, Zwingli, Calvin, et cetera. Basically they believe a bunch of different stuff but they LOVE to banner under the Protestant label.
>What's the difference between Orthodox and Catholic?
Almost no difference.
>What do Christians, normies no you guys, think of Jews?
Christians see Jews in an overwhelmingly positive way. Protestant churches tend to be Zionists, and don't care to convert Jews (for the most part).
Catholics and Orthodox want Jews to convert, you see this message a lot in Catholic and Orthodox liturgy (Latin Mass has a line asking God to remove the Jews' veil so they may be saved; don't know an exact instance in Orthodoxy but they do as well).
>Are there any two denominations in particular that dislike each other?
Protestants really hate Catholics, and for the most part ignore Orthodox as if they didn't exist. I also think that Orthodox see Catholics in a negative light.
Hope this explains, let me know if you have any other questions.