Hello there LWTP. The digital formats you need are Mobi (for Kindle), ePub (pretty well industry standard now) and PDF (for those still reading on PCs, laptops, etc.
Sounds to me that you might need technical help in preparing these. There are experts on this very site who offer extremely good rates (I can recommend one member. if you'd like to drop me a PM or email and I'll put you in touch for advice -- we're in no way connected, by the way, other than as fellow members of Mobile Read).
Also you need a secure payment system in place for credit cards and PayPal, which can be complex and expensive to do properly.
Whatever you do, though, and however successful your wee own store is, you can bet your boots that the huge majority of your ebook sales will be made through the big third-party retailers at varying sales commissions.
You don't say where you're located, but that is a major consideration when wishing to deal with these stores. And some have formatting requirements that go beyond the single process of uploading a single file. An alternative is an aggregator (like
http://www.smashwords.com)) that will automatically format for you and try to distribute to major stores at an 18% commission on gross.
If you'd like to see how your own finished store might look and sell books, visit the bookstore section of my independent publisher's site (linked below) and click on any cover shown to take you to its buying page, download options, book notes, author bio, reviews and free extracts.
Luck with the project, LWTP, and very best wishes. Neil