Open the first app you want to use
Tap the Recent Apps button
Tap the app icon at the top of the app preview
Select Open in split screen view
Choose the second app from the recent apps list or app drawer
Adjust the divider to resize the two apps
To exit split screen, drag the divider all the way up or down
On some Samsung phones, you can also swipe up from the bottom and hold, then select split screen from the app icon menu