What did people in montgomery alabama do to oppose segregation apex?

The people walked instead of riding the bus to oppose the segregation apex. The Montgomery bus boycott was an event in the civil rights movement that happened from 1950's to 1960's. It was a mass protest that ended in the U. S. Supreme court that declared the segregation on public buses unconstitutional. It was sparked by the arrest of Rosa Parks on December 1955.

the people boycotted boarding the buses instead of riding in them

This followed the 1955 incident of Rosa Parks. She refused to give up her bus seat to a white passenger, and was arrested and fined. This led to the Montgomery Bus Boycott (1956) and eventually to the judicial invalidation of segregated seating laws for public transportation.