何に使うの？

what; how many; you-know-what; that; whatsit; what's the expression; what do you call them; what?; hey!

at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although

to use (a thing, method, etc.); to make use of; to put to use; to use (a person, animal, puppet, etc.); to employ; to handle; to manage; to manipulate; to use (time, money, etc.); to spend; to consume; to use (language); to speak

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question