the first thing you do if you are running the free source , is to install the nividia drivers
in mabox controlcenter under hardware you see what you are running free or nvidia
however its very easy to change and setup multi screens , remember you are running manjaro .
sudo nvidia-settings
this wil openen the nvida settings in root , you can now save your settings in the good map and for mabox that is /ect/x11/mhwd.d/nvidia.conf
the right name is always nvidia.conf and make sure it is in the map mhwd.d for manjaro
> if you setup for example 4 screens in xserver display configuration there you see how many screens there are , if you have a card that can run multiscreens , set them how you want them from 1 to 2 to 3 to 4 in the right order , frist apply and than save to x configuration file in the map given above and you are running k’now perfetc 4 screens after reboot.