In 1955 Parks took a seat on a bus just behind the area reserved for white passengers. When the white section filled up, the driver told her to give up her seat and Parks refused.
Parks was arrested and charged and found guilty of disorderly conduct, enabling her to challenge the legality of racial segregation through her appeal.
Today would have been Rosa Parks' 100th birthday.
Rosa Parks interview: http://www.achievement.org/autodoc/page/par0int-1
See also http://www.biography.com/people/rosa-parks-9433715
and the story behind the bus http://www.thehenryford.org/exhibits/rosaparks/story.asp