We previously saw strong signs that Microsoft was working on a "game mode" for Windows 10, but it wasn't exactly clear what that mode would do. Microsoft has since provided some details, via platform engineering head Mike Ybarra.
I suppose an exhaustive breakdown was never on the cards (at least to begin with), but at least Ybarra has confirmed that Windows 10's "Game Mode" will "optimise" one's computer to perform better when a game is running, according to this post from Major Nelson:
Our goal is to make Windows 10 the best Windows ever for gaming. With the Creators Update, we’re introducing a new feature called Game Mode. Windows Insiders will start seeing some of the visual elements for Game Mode this week, with the feature being fully operational in builds shortly thereafter. Our vision is for Game Mode to optimize your Windows 10 PC for increased performance in gaming.
Ybarra does go on to mention the more information on the feature will be forthcoming. Just not right away.
There's also talk of something called "Beam", which will be "one of the easiest and quickest ways to stream your gameplay":
Beam will connect to your Xbox Live account, making it easy to stream your favorite games to Beam and your Xbox Live community. No extra software is needed and viewers anywhere will be able to watch your streams and interact with your broadcast.