The function of the preface is to get readers ready to read the book. It does so by characterizing the content and purpose of the book, identifying or even briefly describing the product the book supports, explaining the type of reader for whom the book is meant, outlining the main contents of the book, showing any special conventions or terminology used in the book, providing support and marketing numbers, and other such. Little else to say here other than most technical books have chapters or sections, and, in some cases, parts. See the chapter on page design for format, style, and design issues for elements such as headers, footers, headings, lists, notices, tables, graphics, cross-references, and highlighting. As you know, appendixes are for material that just doesn't seem to fit in the main part of a book but can't be left out of the book either.
Appendixes are often the place for big unwieldy tables.
Some technical publications have things like warranties in the appendixes. Some technical publications include a section of specialized terms and their definitions. Notice that most glossaries use a two-column layout. Notice too that definitions are typically not complete sentences. Good glossary definitions should use the formal-sentence definition technique as described in the definition chapter of this online text.