وَيُسْأَلُ بِـ«كَيْفَ» عَنِ الْحَالِ
Kayfa asks about condition.
كَيْفَ زَيْدٌ؟
How is Zayd?
A response such as 'well' or 'ill' supplies the missing state. The question does not ask who Zayd is, where he is, or when he arrived; it asks for his condition.
With a verb, kayfa may instead concern the manner in which an event takes place. Its English equivalent 'how' therefore covers both a current state and a way of acting, depending on the sentence.