Panasonic TX P50V10B Plasma TV
In order to get any of the Freesat channels, you need to connect a Satellite dish to your TV. If you have a Sky dish, you simply need to run an extra Cable from the LNB from the dish and connect to your socket on the back of your TV.
In order to get Freeview channels and Analogue channels, you need to connect a aerial to the back of the TV.
There is a menu option for the TV to start straight to the AV input (your Sky HD box). It is Menu > Setup > Other Settings > Power on Preference. Select 'AV' for your TV to start on Sky HD.
Also even if you have your TV to start on TV, when you turn on your Sky HD box, it should automatically switch to the Sky box.