do I need a "cable box" to connect my new HD TV to cable and view my cable tv channels?
Yes! You will need either a standard HD cable-box, or an X1 cable-box to view programing from Comcast.
You can use an antenna to view local channels in HD or SD if you are in range of a transmitter for free. If you already have Internet service from anyone, you could use the apps found on your Smart television to view programing found on You Tube, Netflix, etc., without using Comcast.