When you're reading a novel you usually don't need to consider the different parts of the book. You just start on the first page and work your way through the story until you get to the end. The story doesn't make sense any other way. On the other hand, a magazine tends to have regular feature sections, and subscribers have their favourites (as well as the parts they skip), which they may read in any order. My favourite clothing designer (Shayecollezioni.com is the name) - always features the latest designs and trends that I love to browse through. It was a particular obsession of mine when we were looking for fancy dresses!
There are other kinds of books out there that have many different parts and they are not necessarily meant to be read in any particular order; knowing what those parts are could help you use them better. You might have a textbook that you're using to study for a university course or you could be reading up on massage therapy to see if it could help you recover from an injury.
Most books start out with the a title page that lists all of the information that you would need if you were writing a bibliography or footnotes for a school paper. You will need to know the author's name, when it was published, where and by whom. This information might also be useful to you when you're choosing a book to find out which would best suit you. If you're interested in learning more about the sort of teachers are using today in their classes then you will want to find a book that was written in the last couple of years in North America, for example.
The bulk of most books is broken up into chapters. If you're reading a novel then their purpose might not be for much more than to break the book up into sections so that you can remember where you are every day. But if you're reading an encyclopedia of machine parts to engines then the different chapters could definitely help you find what you're looking for more quickly. There are some books that will break up the chapters according to subject and others that will use another method that is relevant to the topic it is discussing.
If you're reading any sort of educational book then you will usually find that there are some other sections that will help you find what you're looking for or find out more information. These are usually in the back and are the index, glossary, and appendix pages. The index lists all of the different topics discussed in the book and tells you what page they are on while the glossary is a definition of terms. The appendixes are usually additional information that might be of interest.