The Smith Act is a law that was passed in the United States in 1940. It was made to help protect the country during a time when there was a lot of political tension. The law made it illegal for anyone to advocate or try to overthrow the government by force or violence.
Think of it like a rule that says you can't use your words or actions to try and hurt or take over your classroom or school. The Smith Act was put into place to make sure people didn't use their words or actions to try and hurt or take over the U.S. government.
If someone was caught breaking this law, they could be punished with fines or even sent to jail. It was meant to help keep the country safe and prevent people from causing any harm to others.