How did the “flapper” movement for women in the 1920s reflect the new freedoms and transform the image of women in American society forever?

In the culture of the 1920s, the flapper was considered the archetype of the modern young woman. The flapper wore the shortened skirts and shortened hair made popular around the later half of the 1910s. She smoked, drank, and flirted, unlike the women in her mother and grandmother's generations. She was often gainfully employed as an adult, less dependent upon the men in her life. In essence, the flapper was considered sexually and personally liberated, irreverent to old institutions such as marriage and the idea of women as domestic angels with no place outside the home.
Of course, not all old norms died. Most flappers did seek marriages—but they generally sought to have fun in the dating world before landing a husband. Few women kept their jobs after marriage, either. However, the idea of marrying for love and companionship was more popular than in the past. Also, women tended to experiment with sex before marriage, and more available birth control helped make such experimenting at "petting parties" less dangerous.
While the flapper's prominence died with the end of the 1920s and the start of the Great Depression, she left a major impact on American culture that lingered even after the bobbed hair and rolled-down stockings popular to her era were no longer in style. While women still contend with the restrictions imposed upon them by society (especially prior to the 1960s), there are more opportunities for women in the workforce and in the realm of personal relationships than before the 1920s.