Wrote 300 pages without using Pages book template

I used the portrait book nonfiction template. The one that has a puzzle on it. I thought it was appropriate. I can't get the background removed to apply a gradient fill. I was able to put in my image and title and author. Can you walk me through the process of replacing everything on the cover page from the beginning?

I read that EPUB might not approve of my cover if it has too many pixel in it too. That's okay as long as it's there while I'm working on it. I have a preface and notes before my chapters starts and I couldn't see any discussion on how to create a separate section before the chapters. Thank you.

Yes, that was the template that I used. Your solution worked for me. I'm new to deleting objects and using all the different icons available to me. How do I add a page and use roman numerals in my preface?

I didn't know how to use "media placeholder" to make my book flowable to EPUB. I pinned images to my text and they float all over. Do I delete the image and the pin and then place a media placeholder where I want the image to be? And how do I connect three images together so that they stay together? Thank you

How do I create a gallery of images for my book? Thank you