I have not yet published, but I am doing a lot of research while I save up the funds to publish on Amazon KDP.
You'll want to make an account here:
https://kdp.amazon.com
Read over the tutorials on the formatting they want you to use so that you can put your story through their ebook formatting tool. You can go on YouTube and see how people do this, it does take a bit of time. Uploading and publishing the book itself is free. Come up with the price you would like and what selections you will make to get paid by Amazon.
You will want a cover to help your book sell. There are premade book covers that can sell anywhere from $5-$1,000+ each. It's not difficult to find discount ones, just search online for "premade ebook covers." Amazon also has a free tool to design your own cover art. Canva.com is another popular free website to make designs, including ebook covers. They have plenty of stock photos for you to use and they have ones to buy if you want something a little more specific, but $2 for an image is a lot cheaper than paying someone to make a book cover. Be sure it fits your genre so that you sell more books. Books with bad covers don't always sell.
Make sure your work is well edited. If you seek help from an editor, it can be a few hundred to a few thousand dollars. So your options are to edit it yourself or hire help unless you can find a free editor that needs the experience, but that usually doesn't happen. If you have writer friends, they might be willing to read your story and give you some helpful advice.
You will want to think about copyrighting your work. In the USA, it's about $45 per book and instructions must be followed carefully or they will reject your application. I'm not sure what this will be where you are from, but look up book copyright. This way it makes it harder for someone to steal your writing from you.
Books need ISBN numbers (they are not cheap - $75-$300). Amazon can offer you a free one if you want it (I am going to buy my own ISBN because I don't want Amazon having all the rights to my book). If Amazon has an ISBN on your book, you cannot easily remove your book from the Kindle marketplace to sell it somewhere else. You are not allowed to sell your book on Amazon and another ebook website at the same time. Books uploaded to Amazon are exclusively on Amazon in many cases. If you want your book available in different formats like ebook and paperback, you need 2 ISBN numbers. You will want barcodes if you plan on sending your book to retailers. I don't think Amazon requires a barcode, but I suppose it never hurts.
I hope you are able to get your book out there