What is the deference between the book and the movie.What did they

Both versions are good.
In the book we live inside Bianca's head.
In the movie screenwriters gave secondary characters more to do.

They are alot of differences.. For example her mom wasnt the main parent around it was her dad. Wesly and B were not child hood friends/neighbors. Madison didnt exhist in the books. There are alot more. I read the book before seeing the movie and I got to say that I felt the movie was better. :)

The movie was great, but I liked the book a little bit better. There were a lot of differences. Here are a few that I can actually remember. (Warning: Many spoilers)
1) In the movie: Bianca talks about how her dad left her mother years ago and that through her depression, that is when she realizes that she wants to be a motivational speaker. He isn't in the movie.
In the book: Bianca's mom is already a motivational speaker when SHE decides that she wants to divorce her dad. Bianca has a better relationship with her dad.
2) In the movie: Madison is the school's IT girl and gives Bianca a hard time.
In the book: There is no Madison nor is there any character that purposely tries to hurt her.
3) In the movie: Toby turns out to be using Bianca trying to get to her friends.
In the book: Toby is a nice guy that actually does like Bianca but it doesn't work out because he still has feelings for his ex girlfriend.
4) In the movie: Bianca and Wesley share one kiss before they actually end up together.
In the book: Bianca and Wesley have sex many times and have a friends with benefits type of relationship.
5) In the movie: Wesley lives right next door to Bianca and has a decent sized house.
In the book: Bianca and Wesley aren't neighbors and Wesley lives in a large house and has a rich family.
6) In the movie: Bianca gets mad at her friends early on in the movie because she thinks they intentionally befriended her to be their DUFF.
In the book: It took Bianca until the ends for her to tell her friends about being the DUFF and she never got mad at them for being the DUFF.
7) In the movie: Bianca goes to Wesley for help with trying to get with Toby. In return, Bianca helps Wesley in chemistry.
In the book: Bianca doesn't let Wesley know that she is bothered by the word DUFF and she only goes to him for sex when things are going wrong. She uses him as an escape from the troubles in her life.
8) In the movie: Bianca's dad isn't in the movie.
In the book: Bianca's dad is a big reason for her to keep going to Wesley because she fears he will turn to alcoholism when her mom sends the divorce papers.

The only thing that's the same in the book are the names. It's a completely different story.