"How are you?"
Hogy van is a very formal way of asking this question, we usually use it when we're talking to elder people, someone we don't know or important people, who are in a higher position than we are in any way (: Meanwhile, hogy vagy is used among mostly family members and friends.
It means the same thing, i.e. a formal how are you. On the other hand, I'd say it would only be used when there are more people around and you are trying to indicate (also non-verbally) a specific person you are addressing. It also feels a bit colder than asking "Ön hogy van?"
There are some mistakes here. ''How are you?'' in English applies in every situation, as there is no difference. In Hungarian there is different every time. This should be corrected here, as the sentence ''How are you?'' in this case, may be applied in both Hungarian cases for it can be interpreted as such.