Why does it come on?
This light will come on because the engine has lost oil pressure. This is most likely from low oil level. Extended driving in this condition can result in catastrophic failure.
How should I react?
At the first spot where it is safe to pull off the road, shut off the engine and make sure that the oil is full. If the oil is full and the engine is not making any odd noises, drive the vehicle to RNS. If the oil is low, add oil or call a tow truck.