The main difference between the book and the film is the time when the stories occur. The film is a much more modern version: The people fight with pistols and their clothes are similar to the ones people wear today (even though they have a very "interesting" style) and they drive cars. The book's story happens in the median age. The people wear typical clothes for that age and their weapons are swords.
But apart from the time differences there are some details which don't concorde between the film and the book. For example, when Romeo is in the Capulet's garden, the two lovers fall into the swimming pool in the film version. This doesn't happen in the book.
So the two versions tell the same story but each one in a very different manner.
