The simplicity about eBooks is that you can read them literally on any electronic device: From PCs and Mac to tablets, mobile phones as well as devices specifically designed for reading eBooks, called eReaders.
PCs and Mac
The easiest way to read eBooks on a PC or a Mac is the ubiquitous Adobe PDF Reader. However, many online bookshops will suggest Adobe Digital Editions, because it can display both PDF and ePUB formats, the most popular eBook formats, as well as because they can display eBooks that contain DRM (Digital Rights Management) technologies, which generally impose restrictions on the eBooks, such as reading an ebook on another device.
eReader devices are specifically designed for reading ebooks. The reason is that they mostly have eInk or e-paper greyscale displays that resemble better the feeling of reading an actual book (in contradiction with the color screens most tablets and phones have). They usually are smaller, lighter than tablets and because of their displays, their batteries last longer. A single charge might last for a month or longer, depending on the use. They also have enough internal storage to hold thousands of books.
Of course, there are specific apps for mobile devices such as tablets or smartphones. Most notable are Apple’s iBooks and Google’s Play Books as well as other apps, which you can find in App Store and Play Store respectively.