If your engine coolant temperature gauge goes up then it means that your vehicles engine is overheating.
An engine overheating can be caused by a leak in the coolant system such as a leaking radiator or heater hose, plugged radiator, bad water pump etc.
A loss of engine coolant is also possible overtime due to evaporation but it shouldn't happen often.
If your engine coolant is not leaking out or evaporating and your water pump is okay then the thermostat between the radiator and engine that the top radiator hoses attaches too could be faulty.
When a temperature gauge goes up on a vehicle it's an indicator of an overheating issue that needs looked into before you're left stranded on the side of the road or damage your engine by overheating it.