An E-Book can be downloaded as a pdf from your IMO Publishing account directly to your computer. You may have to fill in a purchase code, which can be found in your IMO Publishing Account. You get 2 "copies" to download on different devices if you wish. If you wish more copies, you need to purchase the E-Book again. An E-Book works on a Windows Computer, a Mac Computer, and many hand divices without extra software to make it work.
An E-Reader can only be read through the IMO Bookshelf Software, downloadable from your IMO Publishing account. No extra software is needed to download your E-Reader on a Windows computer, but for a Mac Computer it is best to use a "Windows Emulator". Please visit the Apple.com: https://support.apple.com/kb/DL1837?locale=en_US. After you have installed the Boot Camp (Windows Emulator), you should be able to install and use the IMO Bookshelf software, and download the E-Reader.
For instructions on how to use the Boot Camp Software and other similar Windows Emulators, please go to Youtube and search for "Boot Camp Software Mac".