What are you getting at? Do you mean what parts of the book are not in the film and vice versa?

Well,

The Godfather (Part 1) is based closely on the book. However, said that, all flash back about the young Vito are all filmed in GF2. The entire story about Lucy Mancini (Sonny's lover) and Jules Segal (Doctor) and her, uhh, problems are not mentioned at all during the trilogy.

Nino Valenti (Johnny Fontane's friend) is not mentioned in the movie, although he plays a large role in the book.

There are many other small references, most of which I cannot remember now, that are ommitted from the movie. Eg.

The story about Luca Brasi and that poor baby.

Tom Hagen going to speak to Kay, without Michaels knowledge, to bring her back to the family.

Jules Segal fixing Johnny Fontanes voice and Michaels facial scar.

A better explanation of the Bocchicchio family.

The story of Al Neri joining the Corleone family.

Kay being questioned by the police over the dissapearence of Michael after Sollozzo's murder.

More about Johnny Fontane and his (estranged) wife.

Well, that's a start anyway. Hope that is what you were looking for!