you put the shooting sleeve on whatever arm you shoot with, if you are a righty put it on your right hand if your a lefty put it on your eft hand. the wide end goes up by your shoulder and the thin side goes by your wrist.
I believe they can if they are more of a perimeter shooting type of a power forward, for example I wouldn't be surprised if a power forward like Dirk Nowitzki type wears one.