Most of the ATP for aerobic respiration is produced during the Krebs Cycle, also called the citric acid cycle, which breaks down pyruvate, the end product of glycolysis, to produce ATP. This process is duplicated twice so it can produce twice as many ATP as the cycles that come before it.
Glycolysis produces between six and eight ATP in the first cycle, which also produces the pyruvate, which is turned into Acetyl COA. These COA are processed to produce another six ATP before the remains of the COA is processed in the citric acid cycle. The cycle produces six NADH, two FADH2 and two ATP. The NADH produce 18 ATP on their own, then the FADH2 produce another four to go with the other two ATP produced in this cycle.