You will need to discover a profitable niche or category for the Kindle book that you want to publish.
If you do have an idea for a Kindle book, how do you know it's going to sell and be successful?
Being able to identify whether or not there is a MARKET for what you want to create is one of the most important things to master in making money online. You not only have to know whether there's a market, but if the book idea you have will be PROFITABLE.
Your Kindle book idea may seem profitable, but what about the competition? Is the market or niche too competitive for you? Will you be able to compete with the Kindle books out there that have been around for awhile and are dominating the space?
These are all important things that you need to know before publishing a Kindle book.
This can be done on your own (if you have some online marketing experience, then that's plus), or you can use someone else's method of research (in a course). or invest in a software to help with your niche research (AK Elite. KDP Spy or Kindle Samurai ).
Investing in a software is also not necessary in order for you to publish a Kindle book. I've found many profitable niches without using one, so it can be done on your own (although it does make things much easier and faster) .