it can depend on the model, and ive never used USB on a monitor before but they can have various uses:
if it's USB A it's likely to be a straight extension/hub for usb devices, PC > monitor > mouse/keybaord
daisy chain monitors i believe is possible if they are USB C (i dunno maybe USB3 on an A connector as well), so multiple monitors from one video cable / video port on the PC.
also with USB C lightning you can output video and power for example from a laptop to a compatible monitor, check amazon for portable monitor.
the real answer for your specific monitor will be in the manual, a quick look at the specs online might tell you also.