system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do copper wires and fiber optics (light) transmit data?

 Hi,

I  am currently studying computer networks and I have been reading about  how data is transmitted via copper wires and fiber optics.

I understand the very basics of computers, data, logic gates and binary code.

However,  currently I am struggling to wrap my head around how data can be  transmitted by copper/light? It just does not make sense to me!

Can someone shed light on this?
gpt
Consider that you and a friend are on two hills far enough that your voices cannot carry but within sight of each other. You both have flashlights and know morse code. So by flashing the lights at each other you can send messages (ie data). 

Instead of flashlights, assume you have a wire between the hills and one side has a switch and the other a lamp operated by that switch. You can now send the same data by flicking the switches on and off according to morse code.

Now replace the wire by a long internally reflective tube. By flashing a light on one end, the flash appears on the other, so you can send messages again.

This is how copper wire and fibre optics work - just an agreed upon method to interpret the on-off signals. As long as both parties agree what certain sequences mean, then you can send information.