There are three cables that connect to the back of the Wii U. Plug the AC adapter into an electrical socket. Now take other end of the AC adapter, which is coded yellow, and plug it into the yellow port on the back of the Wii U. Orient it correctly by looking at the shape of the port. Take the sensor cable, which is coded red, and plug it into the red port, whose shape will also show you how it goes in (if you have a Wii that you plan to disconnect you can simply connect your Wii sensor bar to your Wii U; it’s the same connector).
The Wii U comes with an HDMI cable, which is shaped a little like a smiling mouth. If your TV has an HDMI port, which is shaped the same way, then plug it into the TV and you’re all connected.