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..
