N Many GPS's use the serial port, some use the USB port. There may be a driver you have to install. You then configure your Navigation software to let it know where the receiver is and you should be ready to go.

More detail: Some USB GPS receivers simply route the GPS information over to your PC's com port so the GPS APPEARS to be a serial GPS. They do this by installing a small driver known as a USB-serial port bridge. You can then set the com port by right clicking My Computer-->Properties-->Device Manager. Look under the serial port entry and you'll find the serial port bridge (if it installed correctly). Click on driver and then advanced and you can set the com port to the port you would like. You then set that corresponding serial port in your navigation software and the the receiver should work.