Be sure to memorize the general equation for cellular respiration on page 1-9 in your study guide.  Although you may not feel that you really understand the process, at this point all you need to know is that this is the mechanism via which energy is released to do cell work.  All of the characteristics of life are energy requiring processes.  Cellular respiration is an example of a metabolic process.  Although this particular metabolic process releases energy, other metabolic processes are energy requiring.