That's the libusb for Win32 USB library. Keep in mind that if your USB device uses proprietary protocols to communicate you'll need the help of the company that created it to get the drivers to talk to it.
Using almost any port, which USB is, requires interaction with the Operating System kernal. Assuming you are using Windows the the suggestion from cnoeval would work, otherwise we need to know what platform you are writting for.
Also depending on your IDE and\or Compiler suit, you should already have a lib specially built for this.