Self publishing is not that easy. Well... that's not exactly true... it is reasonably straight forward. Doing it well and getting noticed is the issue - and while I know a little about all of this I make no claims to be a master - I am always learning.
Getting published with an Amazon eBook is simple enough. You just need a half decent layout, good spacing, and not too many hard returns. Let's not forget putting up the best cover you can afford and having a kickass blurb for the back. Follow the Amazon guide and review any suggested errors or changes. The paperback is not a big deal really. Just stick to some good guidelines for the layout (Smashwords Style Guide is great - and you may think of uploading it there too).
For ISBNs do a Google - I use Thorpe-Bowker. This is not complex and you will get the hang of it pretty quickly. You can get ISBNs for eBook and paperback. They are not free, bit not that expensive either if you buy them in bulk (like 10 at once).
If you want hard copies to sell (by post, or at markets) or give to others you can get a quote from most printers. Google to find printers in your country - then check them out for cost, quality and delivery timeframes - if possible speak to other authors who have used them. If you're lucky enough to be in the USA, Amazon will sell you "author copies" at a good price with competitive posting charges. Unfortunately, this option is no longer available to me (in Australia) and no doubt not available to others either. In Australia I have used "The Book Print Company" and "Ocean Reeve Publishing" both around the same price for a 50 book purchase. ORP will first send you a single proof copy and wait for your feedback before doing full print run. I like this option. I have had good quality from both.
Consider a book trailer - can be cheaper than you think! Use this with YouTube and other social media. See my other Blog Post on this.
Okay,,,, so you now have your books both online and in the hand. What next?
An author Facebook page is a start. A Twitter and Instagram account is a pretty good idea too. Maybe your own blog.
Know your sale prices and postage costs and plan your book launch.
Post online in all your social media outlets. Post pre-launch, at launch and post launch. Message and email friends and family and ask them to re-post or share. There is a balance between spamming and frequent posting. Your posts should be varied with pics and links to keep your audience interested. Not too wordy. You could consider special sale prices and offers at launch or on pre-order.
At some point you'll be wanting some book reviews that you can use to for further promotion. These can be informal (from Facebook comments; or even verbal comments) but they may be more regulated via Amazon or Smashwords or Apple depending where your book finds itself.
After all your hard work - there are still no guarantees - the struggle continues! And let's not forget you've got another book to write yet, so get to it!