system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a computer learn?
gpt
An analogy is finding your way to the bottom of a valley while blind.

The computer takes a guess as to how to use its inputs to spit out an output, then it gets told how wrong it is. The way you combine the inputs is the position on the ground you are; and if you start from a guess, that means you randomly pick a point on the map.

The wrongness is the height of the ground: less wrong means lower in a valley. Somewhere in the valley, there is the lowest point where you are as correct you can be. How do you get there as a computer if you can't see the whole scenery?

You need to take a step, and feel if you got higher or lower: that is if you were more wrong or less wrong. Taking this stepwise approach, a computer can walk in the direction that leads to lower ground until it gets the lowest point.

At this point, it has come upon the best way to combine its inputs to give an answer that is as correct as it can get.

This is how the computer learns.