You will need to learn the basics of exposure. This means you have to know the relationship between aperture and shutter speed.
To get sharp pictures of racing cars, you will need a fairly fast shutter speed. You could set your shutter speed manually but you will have to open up the aperture accordingly to get proper exposure. Unfortunately lenses can only open so big...so unless you can get close enough to use a flash, or shoot under bright lights...you will get blurry or dark shots.
Also, faster film (ISO 800 or 1600) will make it easier to get proper shutter speeds.