Hi Quan1303, welcome to the WD Community. If you are trying to connect both NAS to each other using a USB cable it wont be possible, the USB cable on the My Cloud is only for expansion purposes and only to be used for USB external storage.
Hi again, with the My Cloud you can create local backups to a USB drive or to another NAS on the same network, these are called “Safepoints”. The kudo star is the button below the avatar picture.
Click on the following link for more information on how to create Safepoints.