Basically, you should think about how to send and receive data wirelessly. A wired connection follows the same logic, but don’t bother with that. Non-ionizing (harmless) radiation is emitted, such as radio waves that are essentially light outside the visible spectrum. When they stream it, it’s “modified” which just means it’s encrypted. How it is encoded by making the frequency fluctuate. When you think of frequency, think of your car’s FM radio. The channel size of 107.6 is basically 107.6 megahertz (MHz), which is just a measure of how fast a wave goes up and down. 107.6 MHz will go up and down 107.6 million times per second. But do you see those zeros at the end? This is where it fluctuates a bit; It could be 107,601,500, a little higher/lower, or anywhere there as long as it doesn’t interfere with the frequency of other channels. These fluctuations are basically code, like how Morse code uses dots and dashes.
The modem can interpret those wavelength fluctuations and determine which code to send. Then the code is run to do its job (sound, data, etc). This process is demodulation. The modem can do this in reverse, broadcasting a response essentially the same way.
I know I said I wouldn’t get into the wires, but here I am anyway. The wires that transmit data do the same thing but with electricity rather than radiation. A .5v is 1 and 0v is 0. This is where 1s and 0s come from in computer code, sort of. Computers use small switches called flip flops that work the same way. If the slipper holds a voltage, it will be 1.
Optical fibers do the same thing, but by using light through a glass-like wire instead of electricity.