Is hydroelectric power is a fossil fuel?

Yes. Coal, Oil and gas are used
Yes. In fact, most of the electricity in the world is produced by burning fossil fuels. The heat from the burning fuel produces steam, which is kept at high pressure, and released with enough force to turn a turbine, which powers an electric generator.

This is not ideal, because burning fossil fuels release excessive carbon dioxide into the atmosphere, which slowly is warming the planet, plus they release pollutants (such as Mercury vapor), that are harmful to the health of humans, plants, and animals.