application & driverstudio

Hi,everyone:
   I use driverstudio to generate a usb driver.
The device has 6 endpoint(2 control endpoint,2 generic endpoint & 2 bulk endpoint)
  In application software,i use OpenByInterface( &ClassGuid, 0, &Error) to open a device or a pipe,i can open the device,but i do not know how to open a pipe.
  please tell me how to open a pipe!!!
        

Best Regards!
                                   r_wind