It's just that Kindle creates an @kindle.com email address for you to file share, with the same handle as the email address associated with your account. eg if my email address associated with my Amazon account were allmywires@hotmail.co.uk, they would create allmywires@kindle.com. You can then send .doc files from amw@hotmail to amw@kindle and you just need a wifi connection to download it.
Cheers! I never even knew my Kindle had its own email address. I'll look into sending my WIP to it.