So, you have the .mobi file for the book (if not, get it here). What next? Here are some options.
Reading on a Computer
Sure, you could just read the book as a webpage – but there are other options. First, I would recommend the Kindle app. This thing runs on everything. Windows? Yep. Mac? Yep. Download and install that sucker and you will be good to go.
Maybe you have an actual Kindle device. In that case, there are several options. Many are listed on Amazon’s Kindle page. Personally, I would go with the USB method. Just plug the Kindle into your usb port and drag the mobi file over.
iPhone, iPad, iPod
Get the Kindle app for your device (see the above link). Once you install that app, connect your device to your computer and open iTunes. Click you iPhone (or whatever) device in iTunes. Under the “apps” tab, click on the kindle app. Then you should see a space to drag the mobi file in. This will upload it to your device.