How to Master Slide Over, Split View and Stage Manager
1 Look for another app
To work in Slide Over, with an app already open, swipe up from the bottom of the screen to reveal the Dock. Look for the app you want to open in Slide Over, either in the Dock itself or in the App Library on the right of the Dock.
2 Drag and move
Drag the second app out of the Dock or App Library onto the screen. It opens in Slide Over. You can move the apps between the left and right side by pressing and holding the “…” icon found on top of the Slide Over window.