no android device found!

hi i am new in unity when i am build game for android show this message no android device found! *make sure USB debugging has been enabled *check your device in most cases there should be a small icon in the status bar telling you if the USB connection is up. *if you are sure that device is attached then it might be USB driver problem for derails please check android sdk setup section in unity manual. and when cancel windows show this couldnt find android device no android devices found.if you are sure that device is attached then it might be usb driver problem for details please check android sdk setup section in unity devial and show this message in console what is solution?how package downloaded?