Easy compared to spending years trying to get agents and publishers to realize how brilliant you are.
This is a list of where I publish my ebooks. Other authors will do it differently, but hopefully this will give you insight in to what an author goes through in this new publishing world.
Before you publish a book, it's helpful to write it . . . After that, I recommend editing it, then editing it again, having others edit it, setting it aside for a couple of months, then edit again a couple more times. There's a good chance you'll still miss a thing or two, but the important part is that you polish it and publish a high quality product. If at all possible, get a professional editor.
You'll also want a cover. If you can afford a professional or semi-professional one, that's good. Otherwise you can make your own with Photoshop, GIMP or some other editing software. The better your cover, the more likely it will be noticed among the countless others. The better the quality of your book, the more likely people will be to buy the next.
At the end of all my stories, I add authors notes with a brief description of me. In it, I also add links to my blog, twitter, facebook and goodreads pages. Then I add short descriptions to my other stories. I have different copies of the author's notes for each store with links to that store. In other words, I don't add Smashwords links to Amazon publications or Amazon links to Barnes & Noble publications.
I write using Microsoft Word, which makes the formatting easy for me. In addition, I write fantasy and don't have a lot of pictures, other things that make it easier. I have a detailed formatting guide here if you need it http://ryallon.blogspot.com/2012/11/publishing-checklist-for-my-book-files.html
Before I continue, I want to alert you to a company you should avoid. Author Solutions and its many tentacles is a company that preys upon hopeful writers. You can learn more about them here https://davidgaughran.wordpress.com/2014/06/03/the-case-against-author-solutions-part-1-the-numbers/
There are the places I publish my ebooks. Others exist and you can look them up.
1. Smashwords. I recommend using the Smashwords Style Guide to format your word document. In fact, it's vital if you want to publish through them. I distribute to Apple, B&N, Kobo, Scribd, and numerous other small bookstores through Smashwords. Due to time constraints, Smashwords and Amazon are the only two I publish to at the moment.
2. Amazon. I make a copy of the Word Document that I used for Smashwords. Then I add page breaks after the title page, copyright page and chapters. After that, I save it as a filtered web document and then convert it using mobipocket. Here is a more specific guide: https://kdp.amazon.com/self-publishing/help?topicId=A17W8UM0MMSQX6
3. Kobo now has self-publishing platform though I use Smashwords. With Kobo, you transform your word document into html by saving it as a filtered web document. Then you use a program such as Calibre to transform it into an epub. You can find more info here: http://download.kobobooks.com/writinglife/en-US/KWL-User-Guide.pdf
4. B&N has a Smashwords version of my novels, but you can publish directly with them if you like. Warning!!! B&N now partners with Authors solutions. If you do publish with B&N, do not pay for any of their services. It's just not a good value. With B&N, you just use the word document used for the others with the exception of specific author's notes and any publishing info. You can find more info here: https://www.nookpress.com/ebooks#
5. XinXii is a European competitor to Smashwords. I haven't used their services, but from my reseach, I personally prefer Smashwords, http://www.xinxii.com/default.php/en
5. Createspace is my favorite for print on Demand Books. I only publish my novels in print, not my short stories. Createspace is owned by Amazon and has been a dream to work with. I make all of my covers to fit their guidelines, with a spine and a back cover. https://www.createspace.com/
5a. Createspace's biggest competitor is Lightning Source, and many of my peers use their service. http://www1.lightningsource.com/
5b. Lulu is the third company that does print on demand books. I'm not certain how good their service is. https://www.lulu.com/s1/paperback_b/r/site
6. Another lesser known place to publish is Scribd. http://www.scribd.com/ You can sell books in PDF form. I distribute there through Smashwords. The site has made vast improvements in recent years. The biggest issue most writers have is its reputation of being a source for pirates to get material, though I don't know how accurate this currently is.
7. There is also a site called Wattpad. http://www.wattpad.com/ They don't have a way for you to sale books as far as I know, but this is an excellent place to publish free books. It's also a good way to get input on your writing, especially if you're willing to join groups and return the favor with other writers. They only accept uploads in .txt, so you'll lose most of your formatting. Links and tables of contents won't work.
8. There is also a site called Obooko where you can put free books as well. In it, you give the readers the right to print out pdf documents for personal use. You can also supply .mobi (Kindle) and epub (everything else) for people to read on ereaders.
Note: All of these sites enable you to retain your worldwide copyrights. You are only giving them the right to distribute or sell for you. None of them prevent you from distributing elsewhere.
There are other sites out there where it's possible to publish ebooks. Look very carefully at there terms and make certain that they don't have any sort of restrictions preventing you from publishing elsewhere, or exclusivity clauses. Publishing your books is an endeavor where you truly want to read the fine print on everything. I recommend hiring a contract lawyer if you're not confident about what you're agreeing to.
I don't publish to Google Documents because they have been known to reduce the price on all books, which means Amazon and the rest are going to price match. This can really mess with your royalties.
Whatever your decisions, don't expect to hit it big right away. Being a self-published author is a LOT of hard work. Not only do you need to write quality books, you have to market them. You can find some marketing tips here on my blog, but those are only a start.
All my best and good luck. :)
John H. Carroll