The easiest way to put books on your Kindle is to do it via email.
To get your Kindle's email address, go to www.amazon.com/myk using your PC's Web browser. Tap on "Your Devices," then choose the relevant Kindle from the gallery below. Next to "Email," you'll find the Kindle's email address.
Now click "Settings" and scroll all the way down to the "approved personal document e-mail list." Click "add a new approved e-mail address," and add the email address you intend to send your books from.
Remember, your Kindle needs to be attached to a Wi-Fi or 3G network for this to work. It doesn't have to be your home network, of course; you can go to a coffee shop or a public library, for instance.