Split View makes it easy and fast to put two applications side by side in a full-screen view. This can be a big help if you need to copy and paste text between applications. It’s a particularly handy feature for iMac users and others who have large screens with plenty of real estate.
There are two ways that you can use the “Split View” feature in OS X El Captain:
Click and hold the green full-screen button in the upper left-hand corner of an application’s window.
The new feature allows you to position the app on either the left or right-hand side of your desktop.
Any other apps that support the new feature will show as available on the opposite side. You just need to select the app you need to bring it forward.
If you are already running an app full-screen, just open Mission Control.
Drag the app over the full screen app space. The view will split, allowing you to select which side to view the app on.
Once in Split View you can resize the windows running side by side. In the middle of the split, there will be a black bar that you can drag left or right depending on which side you want to increase in size.