Assuming you're talking about a standard car with a manual transmission, it takes most people a few days to get used to operating the clutch. The key is to go slowly at first and gradually increase your speed. Many people find it helpful to practice in an empty parking lot or on a quiet street.
It's important to remember that the clutch is not an on/off switch--there is a sweet spot where the pedal is neither fully engaged nor disengaged. Once you find that sweet spot, you'll be able to start and stop smoothly without jerking the car.