If you have broken your arm, you shouldn't change the position of your arm, and you should (must) use a bandage(to immobilize it) and call 999
If you've cut your arm, you should wash your arm with water, use a bandage (to stop bleeding) and call 999 (if injury is deep)
If you've burnt your arm, you shouldn't put butter on the burn, but you should put your arm in cool water or put a cold compress on and call 999(if injury is large)