A book analysis is similar to any other analysis. Refer back to your original instructions, if you have been given any, and you should be able to develop a writing product that reflects a clear understanding of your book. This might involve explaining plot development in terms of both structure and events that help to enhance it. Another element present might be to discuss the different characters present, and how each character is developed and "filled out" through the course of the book. Discussing the elements of literature such as setting and author's style might be another component of a successful book analysis. Finally, I would suggest that if there is a theme or some type of statement being made, this might constitute a strong conclusion point to your book analysis.
When you analyze something, you take a close look at it, examining its elements and how it's put together. Therefore, in a book analysis, you're taking a close look at various elements of your book and considering how the parts come together as a whole.
I sometimes tell my students to think about what they would say if they were talking to someone who'd never read the book, though without going into a detailed description of the plot; a book analysis does not usually include a detailed plot summary. At a very basic level, you'd need to tell them title, author, date/place/year of publication. Then you'd need to describe what makes up the book: theme(s), focus, or perhaps the purpose of the book. Additionally, you might consider reasons that you think the author might have written it. Reflect on your own opinion about the book and consider whether you think the author was successful in what sh/e was trying to accomplish.
Another way to think about it? Consider how they do "gown analysis" on Oscar night. They pick apart each dress, talking about the designer, fabrics, complementary jewelry, etc. In a similar fashion, you'll "pick apart" your book.