(Updated: You'll need a Samsung Galaxy S3, Galaxy Note 2, HTC One, One X, One X+, and now the Galaxy S4 or Sony Xperia ZL in order to use Facebook Home, though any Android phone can currently use Chat Heads.)
Getting Facebook Home takes only a quick trip to Google Play — just install it as you would any other app. Once that's complete, press the Home button on your Android handset. A pop-up will appear asking which homescreen application you'd like to use, and after tapping "Facebook Home" you can select "Always" to make it appear every time you press the Home button, or "Just once" if you want to try it out but keep your regular launcher intact. If you hit "Just once," you'll be prompted to choose every time you press the Home button.
Next, a button in the center of the screen will prompt you to log in to your Facebook account. Once you've logged in you'll be greeted with your Facebook News Feed, though it's laid out slightly differently from Facebook's standalone app. It's called Cover Feed, with updates are converted into full-screen banners. (To get a better idea of how Facebook Home performs, be sure to read our full review.)
Home also integrates SMS and Facebook Messenger, though the two are still technically kept separate if you eventually decide you'd rather use their own apps. Incoming messages appear on your lockscreen as they come in, and tapping on them will take you directly to that conversation. You can also swipe your "bobble" (a circular icon of your Facebook profile picture) to the right on your homescreen to see a list of all your conversations.
If someone messages you while you're doing something else, their Chat Head (a floating, circular icon containing their Facebook picture) will appear, and tapping it lets you see and respond to the message, then quickly go back to whatever you were doing. If you don't want to respond, you can fling the Chat Head to the other side of the screen or slide it down to make it disappear. It's quite fun to play with, and it's really useful.
The Chat Heads feature isn't technically part of Home itself — it's part of Messenger instead. If all you want from Home is the integrated messaging and Chat Heads, just download Facebook Messenger from Play, and they'll start showing up.
Facebook's overhaul of your phone is attractive and fun, but it isn't for everyone — it can make your apps harder to find, and it doesn't support widgets or much customization. The easiest way to remove Facebook Home is to open the app drawer and select "Home Settings," then tap "Turn Off Facebook Home." Android also allows you to go back to your default launcher (or any other one you choose) with ease.
Open Settings by swiping your bobble up to open your bookmarks, then swipe left to access all of your apps. Tap on "Settings" and scroll down to the "Device" category, then select "Apps." This will bring up list of all of your installed apps. Scroll down and find Facebook Home. Tap on the name, then scroll down to the bottom where it says "Launch by default" and select "Clear defaults." Hit the Home button again, which will again give you the option to pick your launcher; pick Launcher, and choose "Always" to make it the default.
You can also just uninstall Home, of course, and everything will go back to normal. Facebook is promising to update Home every month, though, so you might want to keep the app around to stay up to date with Home's latest.