Is Penis Size Related To Successful Intercourse?

hello doctor,am 20 age.,weight 67.so i have one doubt regarding the skin at the penni.how the skin attached to the head of the penni is teared.whether we should do anything in order to tear that,otherwise it will only tear off ah..becoz so many people before marraige they'll do sunthi operation for penni.and also hw much size is required for sex.plz give me clear solution.