Okay kiddo, so Gregory v. Helvering is a very important legal case that happened a long time ago in America. It was about a man named George Gregory and a person named Guy Helvering who worked for the government.
So, George Gregory was a businessman who made a lot of money and he didn't want to pay all of his taxes. He tried to do some tricky things to avoid paying them.
Now, Helvering worked for the government and his job was to make sure that everyone paid the right amount of taxes. He didn't like what Gregory was doing, so he told him that he had to pay his taxes like everyone else.
But Gregory didn't agree with Helvering and he took him to court. The case went all the way up to the Supreme Court, which is like the boss of all the courts.
The judges in the Supreme Court looked at everything that Gregory was trying to do and they said that he couldn't avoid paying his taxes just by doing some tricky things. They said that everyone has to pay their taxes and that's the law.
So, the case ended with Helvering winning and Gregory had to pay his taxes like he was supposed to. That's basically what happened in Gregory v. Helvering.