That depends on which light you are referring to. Many newer vehicles have a dashboard icon that lights up to let you know that it is time for an oil change service. Once you get your oil changed, the light is reset and will come on next time it is due. Other modern vehicles alert you through the computer display. If that light (or message) appears, schedule an oil and filter change.
On the other hand, all vehicles are equipped with an oil warning light. This light tells drivers that the oil level or pressure has fallen below acceptable levels. You can check your vehicle owner’s manual to discern what each light or message looks like for your car. If you see an oil warning light, check the oil level with the dipstick on your engine. If it is low, add the proper type and weight oil so that the level is up to the “full” line on the dipstick. If the situation repeats itself frequently, schedule for service.