How do televisions use radio waves?

In the sense that TVs must radiate photons in at least the visible light spectrum for you to even see what's on the screen, yes, they're radioactive. However, very, very little of this radiation is ionizing radiation (x-rays, gamma rays, beta rays, etc.), and thus is completely harmless to you. The dust collected on the TV's screen because of its static electrical field does have slight amounts of ionizing radiation though, because some of that dust is the naturally produced, radioactive isotope, 222Rn, that's always floating around in the background. Also, if your TV is very old, its X-ray shielding could be compromised, and thus could give you a very small, pretty-much harmless dose of X-ray radiation if you were sitting less than two inches from the screen.