I won't get into a detailed explanation of the larynx here, there are many other sites you can find that will do that for you if you are interested, like this super cool site HERE. What I believe is most important to know about the larynx (other than how to pronounce it)is that it houses, protects and is connected to the vocal folds. If it is tense, your vocal folds will be tense and therefore will not be able to operate freely and properly. For healthy vocal production the larynx should be relaxed, not creeping upward nor forced down. Learning to recognize and correct a tight larynx will help you solve many of your perceived vocal problems. Keep in mind that these are reflexive muscles. If you are tired, sick or emotional they will react in kind therefore allowing them to relax will require keen observation and intention.