Every time you strike a match, burn a candle, build a fire, or light a grill, you see a chemical reaction in action called combustion. 

During combustion or burning of things, carbon molecules in body react with oxygen to produce carbon dioxide and water. During combustion processes, energy is released.

For example, the combustion reaction of propane, found in gas grills and some fireplaces, is:

C₃H₈ + 5O₂ → 4H₂O + 3CO₂ + energy