Kindle Direct Publishing is your avenue to publishing your eBook onto Amazon.
I opened an account, created a profile and read the information about eBook publishing provided on the site.
I then made a copy of the formatted eBook I had uploaded onto Smashwords, and after a few minor changes, uploaded this and my book cover onto the Kindle Direct Publishing site.
Within half an hour, my eBook was available for sale on Amazon in the USA, UK and Germany.
To check for sales and royalties, you go into the Kindle Direct site.
So far, this whole exercise has cost me $147. My eBook is on Amazon in three countries, on the Smashwords site as well as for sale through all their distribution partners.