Is a stress ball recommended? does it actually relieve stress?

It won't do harm: With proper relaxation techniques, stress ball exercises will likely provide you with some benefit, though the degree of benefit varies from person to person. You are only 19 and if already experiencing much stress in your life, i recommend see doc/therapist to find out why and they may provide better stress-relief strategies for you. Otherwise, stress-ball may help and sure won't do you harm. :-).