There are a couple of ways to get the .mobi files of The Story of the World onto your Kindle. This article from the "XYZ for Dummies" series describes the process:
Take a look at this article to learn how to find your Kindle’s email address. When you know the address, open your Well-Trained Mind confirmation email, which contains the .mobi files the Kindle reads. Download the file(s) to your PC or other device. You will find them in your Downloads folder; the files are named *.*.mobi. Then send the file(s) to your Kindle’s email address.
The "Dummies" article describes the process, and it also tells you how you can change your Kindle’s email address to make it easier to remember.
Amazon is very serious about security (which is good!) so the first time you send something to your Kindle, you'll have to add your email address to a list of "trusted senders" so it knows you're not a spammer.
If you have further questions about downloading files to your Kindle, check Amazon’s support page.