Kindle owner's manuals are available online at the manufacturer's website, Amazon.com. On the Amazon Device Support page, select your Kindle model to view the appropriate manual. Depending on the device, the manual can be downloaded or viewed on the device.
If you do not know your Kindle model, you can identify it by opening your Kindle and selecting Settings and then Device Info. If the battery is dead, you can also find the model number on the back of the device or on the original box.
The Amazon.com Device Support page also contains useful Kindle guides and frequently asked questions.