Distributing ePUB eBooks is very simple. You can normally distribute them directly to your customers or users, even if you are targeting Apple iOS/iBooks devices. Unlike iOS apps, you do not have to distribute eBooks through the Apple store, known as the iBookstore. Users can install your eBooks directly on their iPad, iPhone or iPod Touch with the free Apple iTunes program. The same applies to most other ePUB eBook readers, although you should always check for the specific stores or devices you are targeting.
Put the eBook file online and post the URL to the file as a QR code, which can be generated by Help+Manual. Users then scan the QR code with their device camera and the book is downloaded and loaded automatically by the Kindle app (except on Windows Phone). This works for ePUB eBooks and unprotected Kindle/Mobi books for viewing with Kindle apps, except on Windows Phone devices. Kindle hardware readers can only load eBooks via USB or from the Kindle store.
Just like digital music, digital eBook sales are generally more successful if you don't annoy your honest customers with DRM (digital rights management / copy protection).
If you must add DRM to ePUB books you will need to go through a service provider to do this, as it is a complex and expensive process.
You can submit the Kindle/Mobi books generated by Help+Manual directly to the Kindle Direct Publishing program for distribution via the Kindle store. Get started on this Amazon page for information and instructions:
If for some reason you want to or must publish through the Apple iBookstore be warned that it is a complex process that may be expensive. Some authors have found that they do not have full control over where and how their books are made available. Here too, it is recommended that you go through an ePUB service provider, which Apple refers to as "aggregators".