Not quite sure if I got the essence of your question, but I think you mean, how does one generate energy. At its core it’s always a magnet rotating in a spool of conductive wire. The only thing that’s different in every type of power plant is how you get the magnet to spin. In coal or gas planty you burn something und with this heat turn water into steam, which is forced through a turbine, turning the magnet. Nuclear plants use the heat from radioactive decay to make steam and hydroplants (as in you question) move the magnet with the water stream, just like a watermill.
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