Answer:
Rosa Parks was a really influential black woman. On December 1st 1955, she refused to give up her seat on a bus for a white man. At the time, buses (along with many other things) were segregated, meaning black people had to sit at the back and white people sat at the front. If the bus was full and a white person stepped on, the black person closest to the front would have to give up their seat.
However, Rosa Parks decided not to. Her choice got her arrested but it played a big part in fighting for equality and against segregation. For a while after, black people took a stand and collectively refused to get on buses at all, forcing the government to end segregation on buses.
This helps modern society because buses aren't segregated and anyone can use them, and sit where they want.