My father, who has read the book, says that most of what's confusing about the movie is explained by the book is explained by the movie and vice versa. I have neither seen the entire movie in one sitting nor read the book (I have it but have not yet read it) to confirm the veracity of that claim. I have however read up on it and seen all the parts at one time or another, so I recognize most cultural references that I encounter.
I can not only confirm what your father has told you, but I can state that Arthur C. Clarke fully intended that this be so. I've seen clear statements to this effect in an interview. I wish I could offer a link, it is really rather fascinating. The relationship of book to film, and film to book changed somewhat during development, but the book cannot properly be called the original version, or the source material. They were developed in parallel.
By the end of the project, the film and the book had been consciously crafted to complement each other. You only get the full picture by taking both in conjunction. This is part of why I find the film so unsatisfying. I also don't have much appreciation for scenes of vast visual beauty which are not relevant to the plot, so... that explains my distaste for the film. For me it just doesn't tell a story. It merely works as a visual and auditory companion work to the novel. Mind you, although it approaches blasphemy for me to say it, even if the narrative of film and book were presented in medium and style I could enjoy more, I find that Clarke has covered much of the same ground and in a more satisfying way in his other books.
At the same time I have an immense admiration for Clarke and I can't help but admire the work even if I don't enjoy it.
It's an important and fascinating work, but I'll never be able to appreciate it.