TV starts with the CRT
The Cathode Ray Tube was invented more than 100 years ago. A vacuum tube has an electrode at the back, a focusing magnet ring, a metal mesh near the front, and a front surface coated with a phosphorescent material. The electrode is given a negative charge (with surplus electrons) while the front screen is given a positive charge (a shortage of electrons). Since there is no air in the tube, electrons want to jump from the negative electrode in the back toward the positively charged mesh at the front. Some hit the metal mesh and are absorbed. However, there are holes in the mesh and if an electron happens to pass through a hole it continues till it hits the phosphor coating on the inside of the front glass screen. The phosphor glows when it is hit by electrons.
The electrode is surrounded by a cover that only allows electrons to escape in a narrow beam. The magnet ring near the electrode can bend the beam path. In a TV, the beam starts in the upper left corner and sweeps left to right across the top of the screen. Then there is a pause while the magnet reorients and a second left to right sweep occurs just under the line formed by the previous sweep. The process continues until the beam has formed enough lines to fill the screen.
To get color, the front screen is coated with a pattern of tiny dots made of three different phosphor materials that glow red, green, and blue. Three different beams of electrons are directed at the screen. There is only one set of holes in the mesh, but since the three electrodes are positioned at different points in the back of the tube, when electrons from different starting points pass through the same hole they continue at slightly different angles and hit different points on the front screen. The phosphors are laid down so that the straight line from one electrode through all the holes hits only the dots of phosphor that glow red. The other two electrodes are lined up to hit all the green and all the blue dots.
Sometimes we talk about the three electrodes as the red, green, and blue "guns". They appear to "fire" electrons at the screen. This common language has two problems. First, the electrons actually "jump" toward the positively charged mesh rather than being shot from the electrode. More importantly, although the three electrodes are aligned to hit spots of the three different colors, there is nothing "red" about either the electrode itself or the electrons that it generates. Electrons don't have a color. The phosphor on the screen that they hit generates the color.
The light on the screen produces photons. They travel to your eye, are focused by the lens, and strike the cones at the back of the retina. The Red, Green, and Blue phosphors tend to trigger the Red, Green, and Blue cones. A mixture of the three types of light triggers some combination of signals that the brain senses as particular colors. With just three phosphors on the screen, the TV can generate the appearance of any color your eye can see because the eye itself only has three types of color receptors.
Originally the red, green, and blue phosphors were deposited on the back of the screen as round spots. However, if you cover a surface with a pattern of disjoint circles you leave a lot of area outside of any circle. Sony came up with the idea of a Trinitron screen, where the phosphor is deposited in vertical stripes and the spots are shaped as rectangles. Since more area is covered with phosphor, the picture is brighter.
The first mistake that computer people commonly make is to assume that the spots of color on the screen are directly related to "resolution". That would be the ideal situation, but an analog TV doesn't really have a clear "resolution" and a computer monitor supports many different resolutions.
A popular computer display resolution is 1024x768. When the adapter is set to this resolution, it wants to draw 1024 dots on each of 768 lines on the screen. In the adapter memory there are 1024 times 768 memory locations in which are stored the color desired for each of these picture elements or "pixels". The adapter has been told to refresh the computer screen at some rate. At a refresh rate of 70 Hz, the screen is rewritten 70 times a second. Every 1/70th of a second all 768 lines have to be written. Every 1/(70*768)th of a second a line has to be written (ignoring for the moment that there is some special overhead between screen refresh cycles to synchronize things). In that period of time reserved to draw one line, each electron beam has to scan the screen from left to right. The adapter divides the period of time that the beam will scan across the screen into 1024 time periods. During each time period it generates a voltage level for each of the three electrodes to generate the desired color for the currently active pixel. Then it shifts to the next memory location and changes the voltage level for the next pixel.
If everything was perfect, there would be 1024 holes in every line of the screen mesh, and 1024 red, green, and blue phosphor dots on every line. Furthermore, when the adapter was generating the voltage to the electrodes for one pixel, the magnetic ring would be directing the electrons to mostly go through a hole and hit a phosphor dot. Then the physical design of the screen would exactly match the logical resolution of the adapter. However, a computer monitor can be set to many different resolutions, and there is no particularly good way to adjust the timing to target the holes in the front mesh exactly. So instead, the adapter simply generates 1024 changes in the voltage level across the screen without regard to the number or location of holes or phosphor dots. If the beam generated by a pixel spans two phosphor dots, then the pixel "smears" across multiple dots on the screen. Alternately, one phosphor dot can get half its color from one pixel and half from another. Generally your eye doesn't see these tiny imperfections from normal viewing distances.