Although Sal narrates, this is really the story of his friend Dean Moriarity. Dean constantly lives in the moment - experiencing life to the fullest and searching for thrills and satisfaction at each turn. He falls in love and marries and fathers children with no sense of responsibility and no thought of the future. Sal follows along, soaking in the energy that Dean exudes.
They live fast and they observe the sights and sounds and smells of all they encounter; they connect with people; they drink in jazz clubs and feel the music flowing through them. It all sounds great, but there are consequences. Dean is self-absorbed and, although charming and fun, feels no responsibility to others. The ex-wives and children he leaves behind suffer the consequences of his abandonment; and the drug use eventually take a heavy toll on Dean's health.
This was the novel that defined the "Beat Generation" - that inspired millions to dream of freedom from social mores. It is entirely impractical, but it is a wonderful ride.