Difference between 쓰다 and 사용하다?
When do you use one versus the other, or are they interchangeable?

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사용하다 = most used when writing
쓰다 = most used when speaking

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compose, employ, exert, endeavor, wear, choose the site of a grave by  geomancy etc.  Google it in a dictionary.

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What other meanings does 쓰다 have besides "to use" and "to write"?

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쓰다 could be used instead of 사용하다. 
사용하다 could not be always used instead of 쓰다. 
Because 쓰다 has many meanings including 사용하다.

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They are interchangeable very OFTEN, but not always.