So Adolf Hitler scapegoated some groups, how did he convince the people?

First of all you have to understand that Hitler could convince anyone of anything. This can't be stressed enough. But to answer your question about the scapegoats. Europe needed one. It's as simple as that. Especially, Germany. They were experiencing the greatest economic depression in their history. They were angry, tired, and starving and they needed to blame someone for it so it would make sense. The Jews were an easy target for two reasons. One, they've always been hated. For thousands of years before WWII the Jews were persecuted on every corner of the Earth. Anti-semitism has existed almost as long as the Jews have. Two, even though the Jews WERE hit by the depression, many of them seemed to be doing really well for themselves. Some of the wealthiest people during that depression were Jewish families. So it was easy for Christian families to resent them. The others became scapegoats because Germany was ready to believe that Hitler had a plan to make them superior and to never be down and out again. So it was easy for people to believe that some people were inferior and holding the Germans back.