how do fuels provide energy?

Answer 1

Combustible fuels:
energy is stored in the chemical bonds, kind of like how potential energy is stored in a compressed spring. Burning the fuel (Oxygen coming in and tearing apart the bonds and making new molecules) is like releasing all those springs at once for a burst of energy.

Nuclear fuels:
unstable atomic nuclei break apart, shooting off little particles (nuclear radiation) and getting hot. the heat is used to boil water and send the high-pressure steam through a turbine to generate electricity.

Answer 2

When fuels burn they can heat a boiler to drive a steam turbine.