Now you are in charge to monitor your friends activity, so he wont do anything stupid. Gambling sites are so easy to navigate, so easy to register, that even a child can do it. If he asked you for a help, he is either in early ages, or not friendly with pc. Next time he wants to use any device to gamble online, show him some rules, or faq or anything that gives description how betting works. Or even better, find a video about it and show him.