Generally, respiration is the metabolic process by which glucose from food intake is broken down to yield energy output (ATP) for the cell's use. The process of respiration takes place in three major stages namely: glycolysis, Krebs cycle, and oxidative phosphorylation.
In glycolysis, glucose is used to produce a product called PYRUVATE, which enters into the next stage called KREBS CYCLE OR TRICARBOXYLIC ACID CYCLE as acetyl coA. The Krebs cycle, which involves a series of redox reactions, phosphorylation etc is demonstrated in the attached image.