American Pie is about music throughout the 1950s, 60s and early 70s. He begins by talking about "the day the music died," February 3, 1959, when three musical stars died in a plane crash: rock pioneer Buddy Holly, the DJ known as the Big Bopper, and Richie Valens, author of "La Bamba. Elvis Presley was drafted and Chuck Berry was arrested for messing with a prostitute.
"Day the Music Died" = Plane crash (buddy holley)
"Girl who sang the blues" = Janis Joplin
"Father, Son & The Holy Ghost" = John Kennedy, Robt. Kennedy & Martin Luther King.
The "broncin' buck" expression originates from "bucking bronco", a wild horse that is vicious and difficult or impossible to break in, where "bronco" means an unbroken or imperfectly broken mustang and to buck means to resist. (A bronco is an untamed horse)
"I was a teenage broncin' buck" - He was a wild and aggresive hormone driven teenager.