What does a tv tube do?

A "tube," more accurately called a cathode ray tube, or CRT, displays the image sent in through the coaxial cable from the cable box or antenna, or from another video input.

The CRT is a vacuum tube which emits a varying pattern of electrons at the back of a screen. The screen is treated with a phosphor and when the treatment is excited by electrons, it emits electromagnetic radiation, which is light.