Mistress Arya wanted this guy to learn to jerk off because he was a loser and he was not a hit with the ladies. So the only real option which he had was to learn how to jerk off so that he could have fun with himself. Luckily for him, mistress Arya did not just teach him how to jerk off, but he showed him her pussy and her tits and allowed him to watch them as he masturbated.