The narrative in the film Schindler's List differs from the book in three ways: first, the film whittles down the scenes to the present and discards backstory; second, the film puts a priority on visual rather than expository storytelling; and, third, the film shines the spotlight on some of the book's characters.
First, the film deals with current events from the very beginning in its candlelight ceremony opener and doesn't fill in a backstory on any of the characters (except as they tell about their life prior to the war). The book, conversely, provides a fairly standard biography of Schindler's youth in its first few chapters. The book goes into some detail about his early life, growing up in Czechoslovakia, and his years before the war. The film mainly shows Oskar as he is and how he changes due to his internal conflicts over what he observes under Nazi control.
Second, certain scenes in the movie are altered to emphasize visual rather than narrative storytelling. For example, the famous scene of the "girl in the red coat" from the film connects with the same character from the book and expresses the same sentiment, yet her story is told differently in the film. In the novel, the little girl's murder is directly observed by Schindler, which creates a tension and conflict within him. In the film, the internal conflict arises when Schindler and his mistress are riding horses and look down into the town to see people being herded into the Jewish ghetto. One of the people he sees is this little girl, in a red jacket, who will almost certainly die as she wanders through the crowd, with no one to protect her. It is a piece of masterful visual narrative that suggests death rather than shows it, and symbolizes life with its isolated patch of color in a red coat.
Third, certain characters in the film take on greater importance. One example is Helen (a Polish woman, born in 1925) who served as a maid to Amon Goeth. She is a minor player in the book but in the film she becomes a central character and a symbol of Jewish goodness and beauty. When she is brutalized by the vicious Goeth, her fear and powerlessness starkly contrast with the Nazi's violence and absolute power.