A question about God's name?

I have heard(but don't know for sure)that God's name(the hebrew God) is YHWH and that alot of jewish people do not believe in putting vowels in it(such as Jehovah)that it means"I AM WHO I AM" and that it is not to be spoken,what do you know about this?Why do some believe that it is too Holy/Sacred to be spoken?I would appreciate any of your opinions on whatever you feel about God's name,thank you.