First of all, you should observe the oil light when you sit on the driving seat of your car. Turn the ignition for starting the engine and see the oil light that flashes once when you start the car. However, this light turns off after the start of engine but if it does not, then there is some problem with your engine oil.
Immediately turn off the engine and pull the hood of your car for checking the oil level. Use a dip stick for this purpose and pull it out to check how much engine oil is left and determine whether it is sufficient or not.
If it is low, then immediately refill the engine with oil and wait for a few minutes to let it settle in the engine. Now, you should again use the dip stick to check the level of the oil and then start the engine.
Now if the oil light goes off after starting the car, then you have solved the problem. But if it keeps flashing then you have some other problem.
Now you should also check if the oil is leaking from the engine. You can find it easily as it must be falling on the ground or you can also check on the surface of the seal. If the seal is leaking, you will have to replace it.