Got the same monitor as you and had the same questions. So let me give you the basics:
·You need to have Vsync off when having Gsync on.
·The refresh rate does not have any relation with Gsync, you can have any refresh rate with Gsync ON/OFF
·You cannot have ULMB (Ultra low motion blur) active while Gsync is active
·The led light of the monitor (the one next to the power button) indicates if Gsync is active, Red is ON, white is OFF. Its is normal to have Gsync on while on the desktop, its the expected behavior.
I only have one doubt left myself and that is what is the use for the first config button on the monitor, the one that swaps hz with "turbo" mode. I put it on 59hz turbo and still running at 144hz as its the selected in the windows options. Would like to know what's that for without having to read the manual.
Edit: An extra VERY important thing to know. If you let windows turn off the monitor (in the power settings) it will disable the gsync and it wont turn back on once you wake the monitor, so disabled that from power management if you dont want a stroke thinking the thing is broken.
That said.... what a monitor, best upgrade EVER.