TL;DR: The Germans hated the Jews since Europe has a long history of doing so, and because they blamed them for their defeat in WW2 (thx /u/elos_). They apprehended them because they were sense as "cancerous" to society, and because they hated them. What happened? Most of them died. The holocaust is this systematic eradication of the jewish population in Nazi Germany and the various occupied territories. Stupid questions don't exist.

In the words of Carl Sagan:

There are naive questions, tedious questions, ill-phrased questions, questions put after inadequate self-criticism. But every question is a cry to understand the world. There is no such thing as a dumb question.

First of, I am not a historian, but I believe I am well read enough to partially answer your question.

Second, a little bit of backstory:

What is important to keep in mind is that persecution of Jews was not something new in Europe. During the Middle Ages, Antisemitism in Europe was mainly religious and sound like conspiracy theories: It was widely believed that Jews poisoned wells, had killed Jesus, and consumed the blood of Christians in their rituals (despite the fact that human and animal blood are not kosher). During the High Middle Ages there was even a full-scale persecution in many places, with blood libels, expulsions, forced conversions and massacres. Finally around 1500, Jews found security and prosperity in Poland after they were expulsed from Spain, France and the Holy Roman Empire (which covered most of modern day Germany, Spain and Hungary). This led Poland to have the largest Jewish population in Europe, right up until 1933.

In summary, the Jewish population in Europe had it pretty bad for a very long time. This lives on even in our language: For example, a ghetto used to be a segregated part of the city for Jews.

Now, in comes the 19th century, and with it finally some positive change. Due to democratic movements in most of central Europe, Jews slowly but steadily gained the right of christian citizens. Gabriel Riesser, a german lawyer and later the first jewish judge in Germany, fought for religious freedom in 1830 (thx /u/andromedakun), which was finally incorporated in the Grundrechte des deutschen Volkes, the Fundamental rights in the German Constitution, in 1848. It took another 23 years for these changes to occur in most of Central Europe. Antisemitism was not dead by that point, though. During the German revolutions of 1848–49 there were Antisemitic excesses on a massive scale. People blamed Jews for all their sorrows, like many times before outcries for a complete eradication of Jews were common. The rise of Social Darwinism, which are a collection of theories regarding biological concepts of natural selection and survival of the fittest to sociology and politics. The basic idea behind them is that there is a race of humans, the Aryan race, which is superior to all the other races, among them the Semitic and Negro Races, and this superiority means they should rule over all the other races. Note that this is also the time when western nations started a sort of race for overseas colonies, and this theory is basically a justification for ruling over the native population.

Alright, this is Part 1 for now, I have to take a break.