when you say happy and sad, i'm assuming you mean bright vs. dark. i bright sound will come from a firm emboucher and a straight flow of air. a darker sound will come from warm soft air with a slightly looser emboucher, but make sure you aren't playing out of tune. a good mouthpiece will help but that's another story. to bend a note, just drop your jaw and bring it back up. there are two ways to a vibrato. moving your jaw or changing air flow. i'd reconmend changing air flow because moving your jaw will alter your sound and intonation. practice without the horn and then add it in later. just mess around with the stuff and have fun. some of it will just kinda click after while ~firk