Pressing weight overhead makes you stronger. Jerking weight overhead allows you to move a greater load and provides an overload and strength development that pressing alone cannot meet. Good technique is critical, but it is not a substitute for strength. All pressing variations can and should be used when addressing your weak areas—static, push, and jerk variants.
This photo sequence shows a rack jerk done, in this case, from behind the neck. (It can also be done with bar racked on the front of the shoulder, as in a regular jerk.) Because the lifter takes the loaded bar from the rack and doesn’t have to clean it into position for the jerk, it can allow a greater load (and a greater overload stimulus).
Execution of the lift is the same as in the traditional manner, once the lifter gets tight and steps out of the rack with the bar. Upon setting the feet and structure (with a giant breath) the weight is jerked overhead to the extended arm receiving position as the lifter drives his body down under it and the feet out into a split stance. The lifter works to stabilize the load, and then steps the front foot back and the back foot forward (as on any split-style jerk), ending standing erect with feet aligned.