A transmitter sends continuous elecro-magnetic waves. The continuous wave is called a carrier wave. Its frequency is very high. ( It alternates rapidly .) Its pattern is constant. The another entity is the picture-worm from the  caesium cells. Both these go through a modulator. It superimposes the worm shapes over the carrier wave. It is further amplified. It is sent as a signal.

At the same time, another modulated carrier wave leaves the transmitter carrying sound. Its wavelength is different from the video transmission. Thus they do not disturb each other.

At the receiving end, the picture-worm activates a thin electron beam of varying strength in the CRT of the TV set. It strikes the fluorescent screen at the front of the tube to make a tiny dot glow. It traces the first line and then next and next from left to right till the set has received the whole picture and then begins the next one. These pictures move so rapidly that our eyes perceive a stream of them merging into a continuous motion picture.