Dred Scott was a man who was born into slavery in the United States. He lived with his owner in a state called Missouri. Later, his owner moved to a state called Illinois where slavery was illegal. After some time, his owner moved again to a state called Minnesota where slavery was also illegal. While in Minnesota, Scott stayed there with his owner for a little while before returning to Missouri.
When his owner died, Scott tried to claim that he should be free because he had been living in states where slavery was not allowed. However, a decision was made by the US Supreme Court in a case called Dred Scott v. Sandford where they said that even though Scott had been living in free states, he was still considered a slave and wasn't entitled to freedom.
This decision was very controversial and had many consequences. It's important to remember that people didn't believe that slavery was good or right, but some people thought that the US Constitution protected slavery. The Dred Scott v. Sandford decision reinforced that idea and was one of the contributing factors to the start of the American Civil War a few years later.
Overall, the Dred Scott v. Sandford case was about whether or not a man who had lived in a free state could claim his freedom. The decision that was made was very controversial and had a big impact on American history.