Open the first app or window
Hover over the green full-screen button in the top-left corner of the window
Choose Tile Window to Left of Screen or Tile Window to Right of Screen
Select the second app or window on the opposite side
Adjust the divider between the two windows if needed
Press Esc or click the green button again to exit Split View
Use Mission Control to manage or switch between split-screen spaces
Drag a window to the left or right edge of the screen to snap it manually on some macOS versions