I've seen the movie version of this several times and always consider Audrey Hepburn and Holly Golightly as one and the same.
Well the book, or novella, paints a somewhat darker portrait of Holly. The story is told from the point of view of a writer living downstairs from Holly in a New York brownstone. Holly calls him Fred because he reminds her of her older brother. On the outside, Holly seems to be a sophisticated young woman who turned down a Hollywood role and who throws parties in her apartment with many male admirers. But inside, she is really lonely and scared and has bouts of the "mean reds" where she takes solace by visiting Tiffany's. Every man she meets seems to want her, and she uses this to benefit from their attention but she is really just a poor girl from Texas who is really alone. "Fred" seems to take pity on her and wants to steer her in the right direction but things don't always work out that way.
I'm glad I finally read this. I enjoyed Capote's writing style which flows easily and contains a lot of dialog.