I talked about I am Nuclear Energy Engineering student in my introduce post and I will try to explain you nuclear energy.
Everything around you is made up of atoms. In the late 1930s, it was discovered that some particularly large atoms can split in two (or fission), releasing a shockingly large amount of energy. When these atoms were arranged properly in a machine, one splitting atom can cause nearby ones to split, creating a chain reaction.
Such a machine is called a nuclear reactor, and can convert the nuclear energy into electricity, shaft horsepower (for submarines, etc.), neighborhood heating, or lots of other things useful to civilization. Today, nuclear power plants worldwide produce enough electricity to power over 200 million average homes.