Nathan, I suggest you get BookDesigner from the following thread.
https://www.mobileread.com/forums/showthread.php?t=11786 as it has all the bit needed to get to the latest version and it also has good how-to in there.
Also get the BookCleaner files from
https://www.mobileread.com/forums/showthread.php?t=11649 which are also important if you plan on using BD.