Short answers, pulled from the story.
Black Appeal Stations were radio stations that played specific songs aimed at the young African American demographic to keep the airwaves alive during the 1950s. They emerged in the early 1950s as the American radio industry faced total collapse due to the rise of television.
There were 400 Black Appeal Stations by 1956. The number grew from only four stations in 1949 to 200 by 1952 and then to 400 by 1956.
WDIA Memphis was the first Black Appeal Station and it was programmed by Nat D. Williams. The station featured blues great B.B. King and discussed race issues as experienced by black announcers.
Black Appeal Stations played music considered low life because it spoke to the reality of life in juke joints and record stores. The music had suggestive lyrics and double entendres that were ignored by the mainstream but resonated with the African American community.
Black Appeal Stations played upbeat music that combined elements of rhythm and blues, gospel, and country, which Cleveland disc jockey Alan Freed called Rock and Roll. This music was played on numerous jukeboxes in young adult and teen hangouts and defined the next half-century of American music.