tremelo is the proper name but whammi is used as well so it doesnt really matter, tremelo is more to do with the type of bridge it is.
1)screw it in until it is on the last turn
2)hold the bar with a couple of fingers and play a note
3)gently push the bar toward the body of the guitar
this will make the bridge tilt against the body og the guitar changing the length of the strings and flattening the note being played, moving the bar in and out will make a tremelo effect and pushing the bar down is a whammy
hope that has helped
check out www.guitarshredshow.com and look in the lesons section i think it show a few whammy tricks