1. Selecting a channel is tuning; each channel has a specific frequency and the TV knows what frequencies the channel numbers stand for. But what you can't do is tune to a frequency that isn't assigned to any channel, so you would have to select a channel on which no station in your area is broadcasting.

2. You would have to be using an analog TV tuner (which is now obsolete, if you're in the US); digital TV has a much less direct relationship between received radio photons and displayed light photons. On the upside, it's really easy to find a channel where no station is broadcasting, now :) (though actually, I don't know what the new allocation of the former analog TV bands is and whether there would be anything broadcasting on them).

(I've recently gotten an interest in radio technology; feel free to ask more questions even if you're just curious.)