I prefer to work in latex for formatting, but I prefer word processors for writing. So, first I write in a word processor. Then, styles. Then I move to markdown. From markdown there is a which-way adventure via pandoc but for Amazon you need to be able to make an epub. For that I used Calibre and Sigil which was rather daunting in the sense that the requirements are specific for both of those platforms. Once you get that done, you fill out all the little forms for Amazon and BN that include your vendor info, and upload your covers and then await an up to three day approval process.