The buses in Montgomery and most of America were segregated. The front part of the bus was reserved for the white people and black people had to sit at the back.
This meant that black people would pay for the fare at the front, get off and then get on at the back. If there wasn't enough space at the front, black people were obligated to give up their seat to the white person.
Rosa Parks went on the bus as usual and sat exactly where she should have. That day, it was particularly busy. Everyone else in that row got up and moved back except Rosa didn't. She was tired and just wanted to get home.
Rosa refused to get up since she was in her rightful place. They called the police and was arrested. This caused an uproar from the black community that they boycotted the buses in Montgomery.
Please get up so that I can sit down!
Boycott the buses!!!
Black people all over Montgomery avoided using the bus and walked or went by car to work/school. The buses were not getting enough business and were losing money. They had to remove the segregation on buses or the buses couldn't operate. So, the result of the bus boycott not only persuaded lots of other people and states but also marked a step forward in the civil rights movement.