There are three places you should consider self-publishing your book. They’re listed here in order of importance based on maximizing availability and revenue:
Amazon Kindle eBook Self-publishing via KDP = Passive Income ($10)
Always publish in Amazon Kindle eBook format since you’ll receive the widest distribution and greatest revenue from this platform. Note that Smashwords does not publish to Amazon Kindle.
CreateSpace Self-publishing: POD Paperback Books on Amazon ($10)
Publish in paperback via CreateSpace to further expand your distribution and to bolster your Amazon Kindle eBook sales by displaying a more expensive paperback for sale on your Amazon Kindle eBook product page.
Smashwords: Self-publishing eBooks Beyond Amazon Kindle KDP ($10)
And if you’re more interested in availability than revenue, publish on Smashword to effectively publish an eBook everywhere but Amazon (e.g. B&N, Apple, Kobo…). You can not publish to Smashwords and enter your Amazon Kindle eBook into the Kindle Select program.
Finally, if you need a free professional looking book cover, PowerPoint is the easiest tool to use:
Book Covers and Graphic Design with PowerPoint 2013/2016/365 ($10)
I’ll see you in the classroom,