We use wo to ask where someone is. We use wohin to ask where someone is going (direction away from the speaker). And we use woher to ask where someone is coming from (direction toward the speaker). -Wo bist du? -In Wien.

Translation of wen – German–English dictionary whom [pronoun] (used as the object of a verb or preposition, but in everyday speech sometimes replaced by who) what person(s)(?) Whom/who do you want to see? Whom/who did you give it to?

By themselves, wo means "where" and da means "there", but by adding prepositions, it changes their whole meaning. It's important that people learning German understand how prepositions can alter these common words if they want to be understood.