Holden is an underachiever who gets himself kicked out of school. He wanders around the city drunkenly and tries to get a girl to "escape" with him but fails. He eventually gets sick and goes home and back to school. Actually 'Holden makes the decision that he will head out west, and when he mentions these plans to his little sister, she decides she wants to go with him. Holden declines her offer and refuses to have her accompany him. This upsets Phoebe, so Holden does her a favor and decides not to leave after all. '
The main theme of the story is how "phony" people are - in their behaviour. That is, some people will behave differently towards one person than towards another.
The dialogue is rather childish and immature, perhaps that's the point of this book - to get adults to laugh at how stupid children are. That would be quite pointless indeed.
To a greater extent the story is also about angst. He is a failure in school and so he becomes apathetic. He tries to escape but fails at that too. He smokes and drinks. Perhaps some readers will identify with this.
Holden also wants to have sex but fails. Perhaps he just hasn't found the right person. He is also extremely paranoid about homosexuals, which might be normal for a teenager.
The book is a coming-of-age story for Holden as he grows to realise that his initial worldview is too simplistic and warped to adequately describe reality. Holden matures due to his love for his sister.
Overall this book has some good character development and the ending more than redeems it.