Open the two apps you want to use
Hover over the green full-screen button in the top-left corner of one window
Select Tile Window to Left of Screen or Tile Window to Right of Screen
Choose the second app or window for the other side
Adjust the divider between the two windows as needed
Press Esc or click the green button again to exit split screen
If Split View is not available, make sure the app supports it and macOS is up to date