By default display has one screen area which is sized as the display (area 1)
Lanscape displays = 1920 x 1080
Portrait displays = 1080 x 1920
Note! Led screens and other special displays can differ from default
Add new screen ares from + CREATE AREA
Choose the area from the tab and edit the area settings:
Name the area clearly; right or left for example
Set the area size and location
X = the horizontal axis
Y = the vertical axis
Click apply to save the screen areas