Sounds and pictures are displayed on the television (TV) by using electricity in electronic circuits to receive and show these sounds and pictures. The antennae (cable lines can carry signals, too) receive the radio signals and then a cathode ray tube inside the television changes the signals into the electrical currents that paint pictures on the screen. When converted, there are three beams of electrons (electrons are tiny particles that orbit the center of atoms).
The beams are red, green, and blue and make the fluorescent coating on the inside of the screen glow. Pixels (tiny areas or dots that make up part of a picture) cover the screen and when you sit too close you can see them. These dots contain phosphors that glow when hit by the electron beam. The valves found in pre-electronic televisions were replaced by transistors which allowed TVs to be much smaller, like pocket televisions. To see a good explanation of How Television Works, checkout this link!