YOU should read this manual.  If you've decided to publish your book, what does that mean?

It means that you are a publisher.  You're no longer an author.  You need to put on your new Publisher's hat, not your "creative" hat or your "author's" hat. Publishing is a business.  Yes, this means that you have to embrace things that you previously didn't want to; you have to read instructions, learn about publishing, and use that knowledge to ensure that your book is successful, gets bought and read.  

If you're paying a publishing company, like Outskirts Press, a few thousand dollars to do all this for you—then great, you don't have to do what I just said. But if you're on a budget, if  you're paying solely for book formatting—not publishing services—then the onus is on YOU.  You are the publisher, and everything—absolutely everything-from deciding on trim sizes to knowing how to upload your book, to learning about which files are uploaded where—those things are now your responsibility.  Embrace that, and your publishing adventure will go far more smoothly.