Neck lifts are usually performed in combination with a face lift through the same incisions with possibly an extra one just underneath the chin.
The important structures to correct are the skin, the fat, and the platysma muscle. The skin needs to be pulled tighter and the excess removed. The fat is either excised directly or by liposuction.
The muscle is what causes the vertical folds running down from the chin to the sternum in some individuals and is due to separation of this muscle from the midline. This is treated be reconnecting them to the midline by a small incision under the chin, and/or pulling the outer parts tighter under the jaw bone through the standard face lift incision.
The muscle can also be treated non-surgically in some cases.