Today was a big day for Facebook (META -3.63%). For the past week, investors have been scratching their heads wondering what the social network would unveil today at its media event, with the only clue being that it would have something to do with Google (GOOGL -1.46%) Android.

The company introduced Facebook Home, a layer of services that sits on top of Android phones. Shares are up almost 3% following the event, so investors are welcoming Home with open arms (and buy orders).

Facebook Home isn't just an app; rather, it's a set of Facebook's services and features that gets integrated into Android devices. Mark Zuckerberg noted that smartphone usage is predominantly app-driven today. Even when you want to see what your friends are doing, you have to access various apps. Home seeks to put people first.

The company will accomplish this by replacing the home screen and lock screen with what it calls the "Cover Feed," which displays what friends are currently doing. There will also be integrated messaging and notification capabilities. There is still a familiar app-launcher, but friends will take the spotlight.

HTC First. Source: Facebook.

The company has initially partnered with HTC and AT&T (T 0.09%), and the first phone with Facebook Home will be, appropriately, the HTC First. AT&T scored early exclusivity not only with the First, but also with the first batch of Home-enabled smartphones. HTC's partnership is interesting, as Facebook Home would seemingly undermine its own new Blinkfeed feature found on its new flagship One device, which pretty much does exactly what Cover Feed does.

Facebook will also release Home in Google Play to open up all Android devices for integration. The company is also opening up a Facebook Home Program for other OEMs that want to add Home pre-installed out of the box.

Investors are encouraged by the fact that Facebook will eventually, though not at first, include ads in Home. That way Facebook can monetize Home in much the same way "sponsored stories" in its News Feeds have become a revenue generator.