adverb
Broad interrogative adverb asking about manner, method, state, or suggestion. Often used in questions and embedded clauses.
これはどう使うんですか。
How do you use this?
明日の天気はどうですか。
How's the weather tomorrow?
映画を見に行くのはどう？
How about going to see a movie?
Search-only kanji form; not used in modern writing.
こう means 'in this way' or 'like this', referring to something near the speaker or already mentioned, while どう asks 'how' or 'in what way'.
そう means 'in that way' or 'like that', referring to something near the listener or previously mentioned, while どう asks 'how' or 'in what way'.
ああ means 'in that way' (distant from both speaker and listener) or 'like that', while どう asks 'how' or 'in what way'.
The exact derivation is uncertain; it is a native Japanese interrogative adverb related to the ko-so-a-do demonstrative system.