While some Android phones have had split screen multitasking for a while, Android N, or Nougat, is the first to have it built in to the OS. Once Android 7.0 Nougat starts its rollout, every phone with the software installed will be able to take advantage, providing they don't have severely underpowered processors or stingy amounts of RAM.
If you're reading the web, and want to shoot someone a text quickly with something you've seen, or checking Google Maps for an address you've been sent in an email, split-screen could be coming to your rescue very soon. This is how you use it.
How to use Android N split-screen: From an app
There are two ways to launch the split-screen mode when you're looking at an app in full screen. The first way is by just pressing and holding and the recent apps button.
This pushes your app to the top half of the screen and opens up a recent apps selector in the bottom half. Presuming you've not removed the app you're looking for you simply scroll through the cards on that bottom half of the screen and select your second app.
If the app you want isn't in the recent apps screen, hit the home button and then choose any app from your home screen or the app drawer as normal. While you're looking, it pushes the split-screen mode off-screen completely, leaving you with an unobstructed view of your phone.
The second way to launch it requires digging in to settings a little. And it may depend on the phone you have.
Go to Settings > About Phone and repeatedly tap on "Build number" until it says Developer options are enabled. Then, swipe down from the top of your screen, press and hold the settings cog at the top of the notification shade until you get note saying System UI Tuner is added to your settings.
Now when you head to the settings menu you'll find System UI Tuner right next to the Developer options. Go in to the settings, dismiss the pop-up message that comes on screen and choose "other". Tap the "Enable split-screen swipe-up gesture" toggle to the on position.
Once enabled, any time you're in an app, you can swipe up from the recent apps button and it'll smoothly transition to the split-screen.
How to use Android Nougat split-screen: From the recent apps screen
As well as launching from any app, you can launch the split-screen mode from the recent apps screen. All you have to do it drag and drop the desired app from the cards on to the top portion of the screen.
How to use Android Nougat split-screen: Move the split position
By default, Android N split-screen sets the split position right in the middle of the display. Moving it, as you can imagine, is as simple as just dragging it to wherever you want it.
How to: Deactivate Android Nougat split-screen
To deactivate split screen mode, you just press and hold the split screen icon in the bottom right hand corner of your screen.
That's pretty much it. As of right now, Android N is in beta mode, and isn't likely to hit your phone until later this year. If you have a Nexus phone, you'll get it before most. More than likely by October time.