Basically what (/the) ETC and oxidative phosphorylation is, is the products of the Krebs cycle being oxidized and oxygen receiving electrons. And when the phosphorylation part of oxidative phosphorylation occurs is when ADP gains its third phosphate group becoming ATP.
Forgive me for this poor response I was trying to be quick and it resulted in this vague and disorganized mess. To properly explain the ETC and oxidative phosphorylation it would be best to start from the beginning and explain all the stages of Aerobic respiration. Then it would be easier to Segway in to this final stage which would definitely take 2-3 descriptive paragraphs to cover.
