The neck consists of Rotators, Flexors and Extensor muscles. Neck isn't a easy body part to stretch and exercise. You might suffer from tightness in the neck which might be a result of sitting job, and it just might get you nice head ache once in a while, to get rid of this stretching the neck is really most important. Usually those who need neck exercising, by this I mean getting more strength to their neck, usually know how to get it.
As mentioned before, exercising neck isn't as easy as exercising your biceps. There are few exercises for you to try.