An oil leak is a common issue on a car and it can happen at any time. There are a number of place sin which oil can leak out from and it can be hard to diagnose sometimes. Often the only way you know you have an oil leak is when the move the car and find a patch of oil underneath it, or when you check the dip stick and the level is really low.
Ideally the car needs to go up on a ramp for a mechanic to be able to check where the oil is leaking from. Sometimes it is obvious to them and other times it may need more investigation work. It is important not no drive the car too much when you have an oil leak and to ensure that you regularly top it up if you are having to drive it to a garage.
If you have recently had the car serviced then you may find that they have not replaced the sump washer or that they have not fitted it back in correctly. This can cause the new oil to leak out quite rapidly. If this is the case then the garage that did the service should replace the part and the oil free of charge. If your low oil light comes on when you are driving, be sure to stop immediately as driving with no oil will ruin the engine of the car.