Open System Settings
Go to Displays
Select the external display (if using an external monitor)
Turn on Extend display or use a multi-display layout option
Arrange displays by dragging the display icons to match your physical setup
Adjust resolution and scaling as needed
To split one app into two windows: open both windows/apps
Enter Split View (hold green window button or hover over the green button, then choose Tile Window to Left/Right)
Drag a window to the left or right side until the highlighted area appears
Select the second window to fill the remaining side
To exit Split View: drag a window out of the split or click the green button and choose Exit Split View
To split using Mission Control: swipe up with three/four fingers or press Mission Control
Drag a window into the top area to enter Split View, then select the second window