In some electronic devices that have a dedicated reset button in them, how does pressing it actually reset the whole device?
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Chips have lots of tiny information storage elements called flip flops. Each flip flop can store a bit of information (0 or 1). They are used to store things like the current execution point (program counter), calculation results (in CPU registers) and so on.
When you power on a flip flop it can be in any random state. To put a flip flop into a known state it has a reset input. Usually there is some circuitry which makes sure that this reset is pulled once during power up. However, most chips also have an external input for this reset which allows you to pull it from the outside. Pulling it has essentially the same effect as turning the chip off and then on again.
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