Open two different apps, or two windows from the same app, by splitting the screen into resizable views. For example, open Messages and Maps at the same time in Split View. Or open two Messages windows in Split View and manage two conversations at the same time.
While using an app, swipe up from the bottom edge and pause to reveal the Dock.
Touch and hold an app in the Dock, drag it to the right or left edge of the screen, then lift your finger.
If two items are already open in Split View, drag over the item you want to replace.
To give both views equal space, drag the divider to the center of the screen.