The optional formatting choice in most desktop publishing programs is called "facing pages." This formatting choice recognizes that you intend to print your pages on both sides and it attempts to assist you by positioning two text pages side-by-side with binding inside margins and nonbinding outside margins. Often this formatting choice will also mirror page numbers, headers and footers and styling choices from page to page.
The "facing pages" option views individual pages as left or right facing. This can work fine if your document, book or publication can be printed without using signatures. An advanced desktop publishing program may include signature layout as a feature. This allows you to position each facing page on a large sheet of paper based on how the paper will be printed and folded to create the signature. If a document is designed to print with two pages on each side of the paper, the "facing pages" option has to include the ability to recognize how the pages need to be organized. Less advanced software programs may not have this option, making the "facing pages" choice less useful.
A good place to start when you are designing your "facing pages" document is by gaining a good understanding of how your printer operates. Your printer has default settings just like your software program. Read the manual to see what recommendations the printer manufacturer offers for book printing with their device. Some printers will conflict with the margins imposed by the "facing pages" software program and the printed material will vary from page to page which will not look good. By designing your document to conform to the limitations of your printer, you can maximize the finished appearance of your project.
Create a test version of your document by designing 10 pages using the "facing pages" feature. Insert random text with the margin sizes you want, the pagination, headers and other features. Save the document. At the minimum your printer must be able to print on both sides of the paper and it has to be able to collate your pages. Print your test pages. If the result is not good try to have a copier store print it for you. Their equipment has to be compatible with your software program in order to even attempt this print out. If your test document doesn't work well on their printers then you may need to use a different program for the printing system you must use for your project. All of these issues add to the complexity of formatting larger book-style projects.