In English we'd say "My friend IS a student" but Ukrainian doesn't use the verb 'to be' in these cases. E.g. "I am a student" is simply "я студент" [literally: I student]. So I think the dash here is supposed to emphasise that the friend IS a student, a sort of = sign.
I know that Russian has some weird punctuation rules that aren't used in English but are not essential to translate the meaning. Perhaps this is also the case in Ukrainian and this is one example.