It is another way of saying "How are you doing?", which is a way of asking "How well (or poorly) are you doing (something)?" This can be in reference to a specific activity or it can be a general question. In the USA it is more of a rhetorical question. The asker does not expect a detailed answer-- it is more like a greeting, like saying "Good morning". In some other countries, like Germany, if you ask this question you may get a detailed answer-- but probably in German, of course.

aap kase ho .....

it is like a greeting which means both "how r u?" n "i'm fine".

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