I found it fairly easy to make my own book covers for books composed of my own writing.
I opened MS Word and centered the text, made the font large enough that the final product would fit in a single page. The main subject may be in even larger font. I picked the color of the font. Then I added glow from the text effect tool. Then I added background color from the shading tool. Then I printed the screen and cropped the picture to the rectangular size I wanted and saved it and moved the file to documents. With a little experimentation you can make an acceptable book cover for your personal compositions. Please add any further suggestions to this thread. If you have questions over any of this someone would be glad to help.