Hitler first had gain power over Germany. Since Germany was already in a lot of debt, and they couldn’t pay it, he promised to give back the land that they lost back in ww1. He also promised them that he’d make their economy go back to normal. And all this made him so popular till he had full control over them.
Their lives changed because he blamed everything bad that had happened, on the Jews. Since all of Germany had no one else to blame, they believed Hitler. He took advantage of that and killed as many Jews as he could.
He created what’s called the Holocaust. Where he would burn and gas the Jews alive. And he tried taking over the world, Literally! He went to war with almost every country and won but as soon as ww2 came about, he lost all his power.