When you get your ebook (whether purchased direct or as a newsletter freebie), you’ll have an option of two files:
Here are sites with step-by-step explanations of how to send your ebook file to your device:
For Kindle Only (your Mobi file only)
Here’s one site that seems comprehensive with the steps to getting ePub file up for reading:
For Nook, iBooks/iTunes, Kobo, Google Play (the ePub file only), via eBookFlightDeck
Here are other assorted sites:
For Android Users/Nexus, scroll down for instructions on this page.
From Overdrive, using Adobe Digital Editions.