Death of a Salesman is a play about Willy Loman, a none too successful salesman, his wife, Linda, and their adult sons, Biff and Happy and the difficulties within their family. Willy and Biff do not get along at all. Most of the action in the play occurs in the form of flashbacks with Willy displaying some emotional instability, having tried on several occasions to commit suicide.
In Act II Willy loses his job; he is offered a job by his brother Charley, which he is too proud to accept; however, he continues to accept loans from him. In a flashback we learn that Biff had caught his father in a hotel with another woman and become so disillusioned with Willy and life’s possibilities that he gave up an athletic scholarship and a college education. While his sons are home, Willy becomes more and more unstable, and in the end, speeds off in his car. The audience next sees the family at Willy’s poorly attended funeral. A more though explanation and summary of the play can be found at the link below.
There are a number of lesser themes woven into Miller's fine play, but the core theme is what happens when a dream—especially the American dream—dies. Willie Loman wants greatness as intensely as anyone who's ever made it big in America ever did. However, he simply doesn't make it, and all the other themes of the play—the meaning of aging, the nature of family love, etc.—have to be made sense of in relation to this core theme. What does it mean in a land where anyone can be great…to be nobody?
It is a story addressing to the readers painful conflicts within one family but it also tackles other big issues like American national values, and it also examines deeply into the price of blind faith towards the "American Dream", where the main character had high hopes into, but turns out to be nothing, instead to become false dreams and desires.