How does getContentResolver() work?

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http://stackoverflow.com – I had learned some course about Content Provider from Internet. The example shows that how to define a ContentProvider and how to use it. But, I had a confuse that is about use this method named getContentResolver() ,What is this method return? My ContentProvider is not instanced.and the code just write that getContentProvider().query(). I don't understand how does it work. (HowTos)