Click on
Arrangement
and in the default mode (Expanded desktop) click on the new monitor and
drag it as necessary vis-à-vis the Mac monitor. If you select
Mirror displays
the mode will change
to Mirror (the resolution of the monitors will be automatically adjusted according to their
parameters and the highest possible resolution will be set on both monitors). By cancelling the
Mirror displays option you will return to the Expanded desktop mode.
Expanded desktop mode:
The arrow indicates the possible position of the connected monitor vis-
à-vis the Mac monitor.
In the Expanded desktop mode you can choose the Main monitor by dragging the Menu Bar.