The eBooks are PDF (which stands for Portable Document Format) and it means that you should be able to read them on any device including your mobile smart phone, tablets (like iPads), laptops and desktops. Most machines have the PDF reader software already installed, but if you need to install it (often the case on a Apple Mac for example) then you can get the software which is called Adobe Reader for FREE. There is no charge.
Simply visit the official Adobe Website and follow the instructions.