I would say the basic story was the same while most of the plot was different.
The arrival of Aslan was different. He came much sooner in the book. The Pevensies and Trumpkin had already seen him before they got to the How. Peter, Edmund, and Trumpkin all came in the How just as the fight with the Hag, Werewolf, and Nikibrik was starting. In the movie, apart from appearing in Lucy's dream, he first appeared during the duel between Peter and Miraz.
In fact, in the book, the only battle Peter was a part of was the duel and thereafter. The movie he led the failed raid.
In the book, Miraz was king, having usurped the throne years ago. The movie kept him as Lord Regent until the raid, which actually legitimized his power.
MrBob