Living organisims contain cells and within these cells chemical reactions called metabolism occur.
Of course there are two different types of metabolism but I’ll try to give you an easy way of remembering which is which. 
1) Anabolism
Combining of small molecules to form large molecules
e.g.
Photosynthesis – how plants make food
6CO2 + 6H2O => C6H12O6 + O2
Carbon Dioxide + Water => Energy + Oxygen
2) Catabolism
Large or complex molecules are broken down into small, simple molecules.
(I like to think of a cat slashing things up to make them smaller.) 
e.g.
Respiration
C6H12O6 + O2 => 6CO2 + 6H2O +Energy
Food + Oxygen => Carbon Dioxide + Water + Energy
See more about metabolism.
