This may be an oversimplification and I could be wrong but I think it is nothing more than an interface to bridge the high level user software like GQRX (for example) with low level OS software that handles the hardware ports and other items needed to connect with the actual hardware of the SDR radio itself.
I am new to this SDR stuff myself and will be getting a NooElec RTL2832U/R820T dongle soon enough to play with. Already installed the software for linux but still waiting for the radio to be shipped
