The “main body” of your book is the essential part of the content. The frontmatter and backmatter are supplementary to the main text; they provide background and context.
When you decide what material should be in the frontmatter and what should be in the main text, keep in mind that many readers will skip the frontmatter and go directly to chapter one. If your “Introduction” is necessary to understanding what follows, make it the first chapter instead of placing it in the frontmatter. That way it won’t be missed by readers who skip the frontmatter.
If your introduction is not essential to understanding the main text (for example, you describe how you became interested in your subject) then place it in the frontmatter.
The term backmatter refers to everything in your book that follows the last chapter. This may include:
Your book may have some or none of these sections. Like the list of frontmatter, it’s a rare book that needs every single one of these.
Unless your book is creative writing, please think twice before publishing it without an index. To librarians, a book without an index actually signals that the publisher was cutting corners -- and therefore the contents might not be reliable either. An index is an important aid to the reader.