Open the first app you want to use
Hover over the green full-screen button in the top-left corner of the window
Click and hold the green button
Select Tile Window to Left of Screen or Tile Window to Right of Screen
Choose the second app from the other side of the screen
Adjust the divider bar in the middle to resize both windows
To exit split screen, move the pointer to the top of the screen
Click the green full-screen button again on either window
If Split View does not work, check that both apps support it
Use Mission Control or keyboard shortcuts to switch between apps if needed