랑 = and 헐 is not used in formal situations. it is kind of slang, usually used by young people. it's kinda similar with *sigh* in english. situation: someone angered you, and because you are too speechless you can say 헐 someone cant get what you are saying (or when this person is really clueless) and you cant believe how dumb is this person, you can say 헐. it expresses frustration i think..

랑 = and / with 오빠랑 = oppa and/ together with oppa