Yeah, so essentially the TV remote sends the signals down the HDMI cable to the raspberry pi to put it in its simplest terms. If you hold 0 for 3s or something (I have a Toshiba TV, so probably manufacturer specific), the remote then controls the TV the same way it does normally. I think there are HDMI CEC adapters you can buy, but the rpi has it built-in so I've not had to bother, I've been using it for about 5 years I think.