You cannot use the 5V from the USB to power up the transistor and the LOAD because the USB port usually delivers only 100mA, and this is not enough to switch the relay and ... LOAD to the arduino and ...

This Arduino Uno setup can be powered by a 6F22 9V battery or other suitable power source, but it is up to you. The next piece of hardware is a dual-channel, low-trigger, 5V relay module. This relay ...