Open the first app
Swipe up slightly from the bottom to show the Dock
Touch and hold the second app in the Dock
Drag the app to the left or right edge of the screen
Release it to open Split View
Drag the divider in the middle to adjust screen size
To switch apps, swipe up to return to the Dock and drag in a different app
To close Split View, drag the divider all the way to one side
If supported, use Slide Over by dragging the app to the center of the screen instead of the edge