C6H12O6 + 6O2 + 6H2O → 12H2O + 6 CO2
Sometimes the six water molecules are left of the of the chemical reaction (equation). The energy released is trapped in the form of ATP for use by all the energy-consuming activities of the cell. 
The process occurs in two phases or stages: 
       The first stage breaks down a molecule of glucose (sugar) into two smaller molecules (pyruvate) and this is called: glycolysis. This happens in the cytoplasm using enzymes.
       The second stage breaks these two molecules down further using oxygen into simpler molecules of carbon dioxide and water. This happens in the mitochondria. However other chemicals are indirectly made so that hydrogen atoms are freed up used to activate the enzyme ATPase to make the energy molecule ATP which is the main goal of respiration process in cells. Of course, only complex Eukaryotic cells have mitochondria..so respiration in simpler cells like bacteria happens a bit differently.
        Plants have mitochondria for respiration but produce far more glucose (and the sugars and starches formed from it) than they can use as an energy source (but of course use it to builds their cells) and extra oxygen gas since they generally do not have the same energy or material needs for nutrients as animals etc.  Hence the names "producers" and "autotrophs" (make their own "food" themselves without needing to consume other life forms).