A front snap punch is used to strike your attacker in the head from a close distance.
Starting from the fighting stance (shown here with left foot forward) keeping your guard up at all times.
The first strike is using your left fist, this is just a small jab preparing for the next strike.
As you bring your left fist back, strike with your right hand. Be sure to twist your hips to gain extra speed and power.
Twisting on the ball of your rear foot will make it a lot easier to use the power in your hips.