Creating an ebook
You still have to do the hard part, which is actually writing the text; this is just a quick note on how to turn that text into a publishable format which can be published by companies like Apple and Amazon.com. Note that there are many other ebook formats but when I was interested in ebook publishing, I chose to focus on the two most popular: ePub and mobi. Also, the method shown here produces clean and simple formatting, but nothing fancy, for that you'll need to look at the other tools the companies recommend.
LibreOffice - You'll need to copy your text into the word-processor.
Writer2ePub - This is an extension that will convert your text into ePub format.
Sigil ePub Editor - You'll need this to fix any issues you find after the conversion, and to add a title-page.
KindleGen - You'll need this if you then want to convert the ePub book into a mobi book (the format Amazon devices use).
There are other tools needed for the actual publishing, but although I note them below, I'll leave you to follow the recommended practices of the company that you choose to publish under.
Open text as a LibreOffice document, and give it some basic formatting (headers, paragraphs etc) - don't worry about fonts, the conversion in the next step will change them anyway and you can modify them if you need to later.
Using the writer2epub plugin in libre office, convert the document to epub (adding in any necessary metadata).
Open the ePub document in Sigil ePub reader/editor and add in additional info (I like to add attribution to the tools I used at the end as well as include my title page using this tool).
Test ePub document in Apple's iBook proofer.
Using Apple's iBook publisher, publish the ePub book. If you only want to publish with Apple, stop here.
Convert it to kindle format (mobi) using kindlegen as per this example:
kindlegen yourbook.epub -verbose
Preview it using the kindle previewer.
Publish it to Amazon as per this guide.
Apple and Amazon's publishing methods and tools are changing all the time, so be sure to check for the latest versions. Also you're likely going to need an ISBN Number for your book.
Need to add a link to your newly published iBook to your web site? : You can use Apple's iTunes Linkmaker.