Is this feature just not available yet?
I am able to access the swipe left and see a sidebar view but not able to access the half and half, split screen view.
IOS 9 Split screen feature not working on iPad Air 2
Ok, just an app specific issue. It works now for me with native Apple apps, which makes sense.
The App must be prepared for this feature. You must provide a storyboard file as the launch screen, then the App will take part of this new split screen feature.
But there are still some issues with this new feature. For example UIPopoverControls do behave strangely when the App only has half of the screen.