How are nuclear fuels currently used?

Nuclear energy is just another way of producing electricity via a nuclear reactor.

Most reactors use uranium fuel enriched slightly to about 3-4 percent U-235, in the form of uranium dioxide UO2. Some older reactors used metallic natural uranium, while some other reactors use...

For producing electricity

Uranium mainly Plutonium and Uranium in fission weapons, Lithium deuteride in fusion weapons, occasionally small amounts of Tritium gas to boost fission weapons with fusion.

To produce electricity