The New AppleTV acts as your homes "control center" for all Homekit Accessory devices you have in your home,things like lights/locks/thermostats etc.
The New AppleTV allows you to remotely control these Homekit devices whilst you are away from your home with your iPhone/iPad/iPod.
Here is a list of Homekit products available:Apple HomeKit Accessories
With each Homekit accessory there is a companion App that you must install on your iOS device that allows you to control it.
Here is a list of Homekit Apps available,please select the App or Manufacturer that matches your Homekit Accessory: Homekit Companion App List