The first thing you need to do is set up a F.R.E.E. account with Amazon Kindle. Go here to do that: https://kdp.amazon.com
By setting up your Kindle Direct Publishing account you will be all set to begin writing your Kindle books and publishing them to Kindle.
There are some rules you must follow and be certain that you read and heed these rules. You can find the Kindle Terms of Service. Go here for details: https://kdp.amazon.com/self-publishing/help?topicId=APILE934L348N