If you have an Apple TV (3rd generation or later) with software version 7.0 or later, you can control your HomeKit-enabled accessories when you're away from home using your iOS device.
Sign in with the same Apple ID on your iOS device and Apple TV, and you'll be able to use Siri commands to remotely control your accessories.
The support document also outlines how to setup and get started with HomeKit. HomeKit accessories require a separate app download, which you can find in the App store. Once the app is downloaded, you must pair your accessory to your iOS device use a special pin code. Once paired, you can use Siri to control your accessories, group your accessories together, and more.
Apple has also issued a separate support document that highlights HomeKit accessories. We wrote about some of those accessories yesterday including those from Elgato, Lutron, iHome and Ecobee.