for a start,did you check how much oil was in your car in the first place,what made you think it was low,did the warning light come on,have you got a leak,just putting extra oil in your car for the sake of it will do the engine no good at all,if you have overfilled the car with oil,you will need to take some out via the sump plug and check the levels via the dipstick,by the sound of you,you dont really know much about cars,so i would get a mechanic to check it for you before you do some permanent dalmage to the car.