Hello,
If you want to have the output log from u-boot. You just need to connect the USB for the serial communication into your computer and with a serial terminal open the COM port that your computer assigned. Just remember that the default supported baud rate is from 115200. Having that set that connection you could see the output log from u-boot during the booting process and during the UUU debugging process.
Hope that was the information that you were looking for.
Best regards,
Diego.