1998 Jetta wondering question

I've just got this Jetta and when its real cold there is a light that will come on and flash what is this,looks like a temp guage.What is it and what is the fuction thanks Mitch

My Jetta is a 90, so is very different, but... some later model cars have a sensor to check whether the coolant level is low in the 'overflow' reservoir. The flashing might indicate it is low enough to flash, until the engine warms up and the coolant expands into the overflow reservoir somewhat. On Saturns that is usually the reason, or alternately that the sensor is gummed up.
A steady 'thermometer' light would of course indicate an over-temp condition of the cooling system. The function of that light should be explained somewhere in the owners manual.