Powering the base HAT

Hi, sorry for newbie question. I have the LTE base hat attached to RPI4 board. Do I need to to power BOTH the RPI board and the HAT separately? Or just power one or the other?

No. Just power up the Raspberry. But you need to connect one of the the USB ports of the Raspberry with the Micro USB port of the Base Hat with the included short usb cable.