You can publish a book through Amazon using Kindle Direct Publishing (KDP):

1. Prepare your manuscript
Format your manuscript and create your book's front, body, and back matter. You can use Kindle Create to help format your book.

2. Publish your book

Enter your book's details, including the title and author

Upload and preview your manuscript and cover

Select your publishing rights and list price

Choose whether to publish your book in print or digital formats

3. Promote your book

Use KDP's free marketing tools, such as:

Kindle Unlimited to offer your eBook

An author page to share information about yourself and your books

Amazon Advertising to reach more readers

A+ Content to enhance your book's detail page

Here are some other things to consider when publishing a book through KDP:
You can create all formats of your book in your KDP account and link them together.

You can buy an ISBN or get a free one through Amazon