Your book description is a key piece of your metadata.
Book metadata are the words and phrases that you use to describe your book. Your book metadata will consist of basic things such as your title, author name, author bio, book description, publication date, etc. This is the kind of stuff people use when they KNOW what they are specifically looking for. Like your friends and family. They know your name, so they would use that to look up your book.
Keywords are used to indicate the content of your book. Simply put, metadata and keywords are what make your book appear when a reader searches for a particular type of book. So this is the stuff that people use when they DON’T know your name or your book. They only know that they want a book on topic XX. Amazon allows 7 keywords. Keywords can be a single word (not recommended) or you can pack words into a single keyword phrase. Never use those spaces for your name or words from your book title, nor your category.
More information on Keywords:
How To Choose the Right Kindle Keywords and Reach More Readers
Your category is based on BISAC codes. Amazon doesn’t use them exactly, but it will help you to have solid categories chosen. The full list of codes is here: https://bisg.org/page/BISACEdition
For additional reading on metadata: https://www.ingramspark.com/blog/the-basics-of-book-metadata-and-keywords
Your book description appears on the back cover, as well as in the book description section of all the online retailers. You can use the same one or write up several (there are good reasons for having several… it can show you if one gets a better response than others, and can increase your SEO on your website, plus if you have them already done, it’s easy to send out the appropriate one during the marketing phase).
You should have one that is an elevator pitch style – punchy and short. One or two sentences that distill the essence of the book.
A short description: No more than a paragraph or two. This is appropriate for the back of the book, which should contain no more than 300 or so words.
A long description: You have up to 4000 characters on Amazon. It’s a good idea to use as many of them as you can, where appropriate. You can include addition bits like reviews.
There’s some great info on the web about writing book descriptions, but you can start here if you like: https://jerichowriters.com/amazon-book-descriptions-sell/
It’s a good idea, if you’re doing this all yourself, to format your Amazon book description prior to getting into the KDP interface. They only give you two lines so it’s hard to see what you’re doing.
You can find the code generator here: https://kindlepreneur.com/amazon-book-description-generator/
Keep all of these in a Word file so they are easy to find, and have both the plain text version and the coded one.