Dred Scott was an African American. He was a slave.
Dred Scott lived in free states for many years with his owner. When his owner died, he moved back to Missouri with his family where he was considered a slave again. This was not right.
Dred Scott filed a law suit to be considered a free man from slavery.
Dred Scott lost the case. It was decided that a slave was considered property and that slaves did not have a citizenship. It was also decided that Congress didn't have the right to decide slave states.