All techniques, either by hand, foot, elbow, knee, or head, are executed using either of two actions: snap or thrust.
In a snapping technique, the foot, hand, etc. is quickly whipped out at the target. After it makes contact, it is just as quickly retracted. A thrusting technique is similar to a snapping technique except that extra motion is added to make the technique penetrate the target. The snap is quicker than the thrust so it makes it quicker to execute a follow-up technique. To illustrate the difference between a snap and a thrust, imagine kicking a drywall in a room. A snap kick will break through the wall quickly with minimum penetration. A thrust kick will break the wall and penetrate beyond the wall, possibly breaking through the drywall on the opposite side of the wall.
Students are usually first taught thrust actions using hand techniques, while snap actions are usually first taught using kicking techniques. As students progress, they are taught thrust kicks and hand snap techniques. Both methods are effective and each has its place and time to be used.