Open the two apps you want to use
Hover over the green full-screen button in the top-left corner of one window
Click and hold the green button
Choose Tile Window to Left of Screen or Tile Window to Right of Screen
Select the second app or window from the other side of the screen
Adjust the divider between the two windows by dragging it
To exit split screen, move the pointer to the top of the screen
Click the green full-screen button on either window