Understandable explanation to a simple file writer?

I have been looking around the internet for a long time and i STILL havent found a sensible answer as to making a program that creates a file in a directory (Such as C:). So if you could please explain to me how i would do this it would be greatly appreciated! Thanks!
EDIT-Im using java and i want to write a text document. Probably should have said that before :/

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