Being able to view two applications side by side on one screen is something I have found useful on my PC. Until Android N (Nougat) this was not easily available on across Android devices. Now it’s a reality.

When would you use it? 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 useful to you. Read on to see how you can activate and use it.
Launch split-screen
There are two ways to launch the split-screen mode when you're looking at an app in full screen.
From an App
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.
From Settings
You will need to dig in to settings a little. It may also depend on the phone you have, for example on the HTC M9 System UI Tuner cannot be enabled.
But you can try! 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.
If that step works, 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.
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.

Deactivate 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.