#1
Ok... so i wanna kno the use of the tremolo arm... and wht kinda music is it good for???
#2
It's used in all kinds of music. Pushing it up and down slightly will result in a vibrato, used in blues and rockabilly. More extreme bar abuse is featured in rock and metal solos. Pushing the bar down so that the strings become completely loose is used at the end of a phrase. This is called 'dive bombing'.

Check out how this guy does it: www.guitarshredshow.com