Almost Famous begins with eleven year-old William Miller and ends with a fifteen-year-old William Miller. These two William Millers are completely different people, and this difference comes about primarily from this kid's exposure to rock and roll.
When William's sister Anita leaves home, she plays a song to explain her decision: it's "America" by Simon and Garfunkel, and it appears on the record Bookends, the very album that Elaine previously caught Anita trying to smuggle into the house. We know that music is a huge part of Anita's identity, so it's significant that she left her record collection to William. "Look under your bed," she tells him. "It will set you free."
We watch William see go through these albums for the first time. Flipping from The Beach Boys and Led Zeppelin to Jimi Hendrix, Bob Dylan, Joni Mitchell, and more, William finally lands on The Who's "Tommy." Inside, he finds a message: "Listen to Tommy with a candle burning, and you will see your entire future."
In this moment, young William blossoms into slightly less young William, who eats, sleeps, and breathes nothing but rock and roll. The gift of Anita's record collection symbolizes this transformation, the catalyst for William's evolution into a lover of all things rock and roll.