The way in which this functionality works seems simple enough. If you have multiple computers, you can start using In-Home Streaming now. The only thing you need to do is login on Steam on two computers that are in the same network and the computers will connect automatically, letting you install, launch and play games remotely.
What does this mean exactly? If one of those computers is a low-end PC (such as a laptop or a media center PC) or runs a different operating system (such as Mac, SteamOS or Linux,) you can use it to stream games from the more powerful machine.
For more information about Steam In-Home Streaming visit Steam.