How to use Split View on Apple’s iPad Air 2

2. On this panel are app icons. Scroll up or down the panel until you find the second app you want to open. (If an app is already open in the panel and it is not the one you want, swipe down on the horizontal bar at the top of the panel to access the full list of available apps).

3. Tap on the icon to open it. An abbreviated view of the app will appear in the panel, but you should be able to access its controls and use it. While you are using it, the app on the left will dim and become inactive. You can switch back to the initial app by tapping on it. This will hide the right-hand panel again.