Some questions about как and что
I briefly understand that как roughly means 'how' and что means 'what'. But, in the question
"Как ваша фамилия?", why aren't we using что instead of как? I understand that "Как тебя зобут?" can be read as "How do [they] call you?", but what about "Как ваша фамилия?"?
Thanks so much as I have been only learning a little bit of Russian.