How do living things make use of the energy stored in food molecules?

             The energy stored in food molecule (glucose) is released in he process of respiration. 

Explanation:                     Respiration is a cellular process in which glucose molecule is broken down into carbon dioxide, water and ATP is produced as end product. Respiration consists of following main steps:
1. Glycolysis:                It occurs in the cytoplasm of cell, and each glucose molecule is converted into two pyruvates with help of ATP.
2. Formation of Acetyl coenzyme A:                                                        It is a connecting link reaction between glycolysis and Kreb cycle. In this phase Each pyruvate react with Coenzyme A to become acetyl coenzyme A.
3. Kreb Cycle:                   It occurs inside mitochondria. In this cycle each acetyl coenzyme A with fixed with CO to produce citrate which undergo in a cyclic reaction to produce ATP and NADH. . 
4. Electron transport chain:                                           It is the last step of respiration which complete in mitochondrial membrane. In this phase most of the energy is produced along with H₂O as by product.