Electronic publishing, also referred to as ePublishing, is the digitisation of books, magazines etc in order to publish them online and make them more easily available. EPUB is a widely used open source format which allows books to be published zipped folders. These folders hold a range of information about the books look and layout. CSS style sheets tell the end users devices how to display the data, and using the book format is easily transferable to other devices without having to use the EPUB format.
There are free open source ePub publication programs, such as Sigil, which make the process of creating, managing and distributing an ebook that much easier. Equally free online word processors such as Scrivener which allow the creation of workflows to aid the creation and management of epublications.
WordPress.org is a free cloud hosted blog application, it differs from wordpress.com due to the fact that with the former you need to have arrange you own hosting.