how to use arduino with 9v battery

Hello does anybody know how do I use my arduino UNO without USB cable ??? bye using 9V battery I get an error: "Serial port 'COM3' not found"

Thanks

Depends what you mean by use.... to download a sketch you need to be hooked up to the PC with the usb, but the Arduino will run the previously downloaded sketch when it's powered from a battery into the jack. At that stage the PC doesn't need to see the Arduino...

ok, I'm using the arduino UNO+WIFI shield to turn on led, by a website, the quetion is do I have to use the USB cable to run the arduino program ? or by any way I can use the 9v battery ? (by setting the serial port or something..)

I really appreciate any help you can provide.