Mac users who were around for the introduction of full screen mode in OS X Lion remember that this isn’t how it used to be. This option, which is enabled by default on new OS X installations, allows a different full screen app to occupy each display in a multi-monitor configuration.

To see if this is what is causing your issue, head to System Preferences > Mission Control and find the box labeled Displays have separate Spaces. While there could be other more serious problems with your Mac or OS X installation that account for this difficulty with Split View, we’ve found that most users simply need to make a change to the way that Mission Control works. But after upgrading to El Capitan this week, many users report that they cannot get Split View to work at all. Split View in OS X El Capitan allows users to place two full screen apps (or two instances of the same full screen app, like two Safari windows) side-by-side, enabling the apps to take advantage of your Mac’s entire screen real estate while still allowing for productivity-boosting reference or copying between apps. If that feature is Split View, we might have a quick and easy solution for you. But you quickly realize that one major feature, perhaps the one you were most looking forward to, isn’t working. So you’ve just upgraded your Mac to OS X El Capitan, and you’re eager to try all of the new features that Apple packed into this year’s operating system update. El Capitan's Split View Not Working? Check This Option in System Preferences

Mac os x split screen