Logic gates send along signals. A positive charge is a 1 and no charge is a 0 in binary codes for numbers and letters. If a gate is controlled to send along a charge or signal, it goes to another gate. If not controlled to send along, it stops. The control can be a slight charge from another gate or gates. This is the basis of a transistor logic gate made of semiconductor elements on a silicon substrate.
Thousands, millions and even billions of logic gates can be printed together to make integrated circuits, and central processing units in computers, in video chips, and in monitors.
Signals are coming from magnetic recordings in disks and solid state memory. The signals can be programs or data controlled by programs. More information can come in by keyboard or mouse, or by wire, or by radio, by disks or flash drives, from humans or Internet.
The CPUs manipulate the data and send it on to video circuits. There the circuits coordinate them into pictures to be sent down the video cable.
At the monitor, the signals arrive in order. This will be a "raster display" of horizontal bands and vertical columns. Many are done very fast to make motion images. A series of still pictures look to human eyes as continuous actions.
In modern monitors, rows and columns of small patches called picture elements or pixels are in front of a bright flat white panel of light. Each patch is a liquid crystal, a material that twists its molecules if electrically charged. If no signal goes to it, light is blocked. If a signal of some strength goes to it, light passes. Either some or all of it can pass.
Each pixel is in a group of 3. There are red, green and blue ones, usually. Rarely there are yellow ones too. Varying amounts of the colored light are passed through those primary colored pixels, making a whole range of blended colors, a full spectrum of millions of color possible.
So the gates send signals, the video system puts them out in order to make a raster picture, the pixels are controlled to pass light to make images our eyes and brains interpret as complicated moving images.
Watching this whole process change from crude analog images in early television 70 years ago into the all digital electronic systems of recent years. Teaching people how to use computers to make complicated tech drawings. Repairing computers and sometimes, video systems like digital TVs and monitors.